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 $118.81   6.541%   $126.5814   $126.58   $126.60   $126.60  
  Purchase #2 $124.47   13.218%   $140.9224   $140.92   $140.90   $140.90  
  Purchase #3 $179.93   13.678%   $204.5408   $204.54   $204.55   $204.50  
  Purchase #4 $62.27   11.542%   $69.4572   $69.46   $69.45   $69.50  
  Purchase #5 $129.77   12.814%   $146.3987   $146.40   $146.40   $146.40  
  Purchase #6 $88.29   9.190%   $96.4039   $96.40   $96.40   $96.40  
  Purchase #7 $44.97   7.821%   $48.4871   $48.49   $48.50   $48.50  
  7 purchase totals = $748.51       $832.7915   $832.79   $832.80   $832.80