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 $245.91   9.240%   $268.6321   $268.63   $268.65   $268.60  
  Purchase #2 $37.67   10.315%   $41.5557   $41.56   $41.55   $41.60  
  Purchase #3 $129.76   9.122%   $141.5967   $141.60   $141.60   $141.60  
  Purchase #4 $177.92   12.622%   $200.3771   $200.38   $200.40   $200.40  
  Purchase #5 $235.95   3.215%   $243.5358   $243.54   $243.55   $243.50  
  Purchase #6 $68.78   7.244%   $73.7624   $73.76   $73.75   $73.80  
  Purchase #7 $181.71   13.818%   $206.8187   $206.82   $206.80   $206.80  
  7 purchase totals = $1,077.70       $1,176.2785   $1,176.29   $1,176.30   $1,176.30