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 $100.43   10.339%   $110.8135   $110.81   $110.80   $110.80  
  Purchase #2 $236.75   5.649%   $250.124   $250.12   $250.10   $250.10  
  Purchase #3 $155.96   11.111%   $173.2887   $173.29   $173.30   $173.30  
  Purchase #4 $182.48   6.490%   $194.323   $194.32   $194.30   $194.30  
  Purchase #5 $108.69   8.519%   $117.9493   $117.95   $117.95   $117.90  
  Purchase #6 $9.38   8.806%   $10.206   $10.21   $10.20   $10.20  
  Purchase #7 $143.58   6.828%   $153.3836   $153.38   $153.40   $153.40  
  7 purchase totals = $937.27       $1,010.0881   $1,010.08   $1,010.05   $1,010.00