Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $226.96   13.692%   $258.0354   $258.04   $258.05   $258.00  
  Purchase #2 $216.86   5.113%   $227.9481   $227.95   $227.95   $227.90  
  Purchase #3 $132.56   12.727%   $149.4309   $149.43   $149.45   $149.40  
  Purchase #4 $183.37   12.354%   $206.0235   $206.02   $206.00   $206.00  
  Purchase #5 $103.40   11.864%   $115.6674   $115.67   $115.65   $115.70  
  Purchase #6 $118.40   8.816%   $128.8381   $128.84   $128.85   $128.80  
  Purchase #7 $188.77   13.446%   $214.152   $214.15   $214.15   $214.20  
  7 purchase totals = $1,170.32       $1,300.0954   $1,300.10   $1,300.10   $1,300.00