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 $155.35   12.401%   $174.615   $174.62   $174.60   $174.60  
  Purchase #2 $213.45   4.490%   $223.0339   $223.03   $223.05   $223.00  
  Purchase #3 $191.28   8.207%   $206.9783   $206.98   $207.00   $207.00  
  Purchase #4 $22.64   8.485%   $24.561   $24.56   $24.55   $24.60  
  Purchase #5 $211.59   12.369%   $237.7616   $237.76   $237.75   $237.80  
  Purchase #6 $88.65   9.397%   $96.9804   $96.98   $97.00   $97.00  
  Purchase #7 $183.54   11.113%   $203.9368   $203.94   $203.95   $203.90  
  7 purchase totals = $1,066.50       $1,167.8670   $1,167.87   $1,167.90   $1,167.90