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 $248.60   6.611%   $265.0349   $265.03   $265.05   $265.00  
  Purchase #2 $121.56   6.625%   $129.6134   $129.61   $129.60   $129.60  
  Purchase #3 $141.90   7.811%   $152.9838   $152.98   $153.00   $153.00  
  Purchase #4 $6.62   6.671%   $7.0616   $7.06   $7.05   $7.10  
  Purchase #5 $58.68   7.834%   $63.277   $63.28   $63.30   $63.30  
  Purchase #6 $74.33   10.670%   $82.261   $82.26   $82.25   $82.30  
  Purchase #7 $192.64   6.396%   $204.9613   $204.96   $204.95   $205.00  
  7 purchase totals = $844.33       $905.1930   $905.18   $905.20   $905.30