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 $189.57   4.764%   $198.6011   $198.60   $198.60   $198.60  
  Purchase #2 $59.67   5.758%   $63.1058   $63.11   $63.10   $63.10  
  Purchase #3 $34.73   6.716%   $37.0625   $37.06   $37.05   $37.10  
  Purchase #4 $205.57   10.716%   $227.5989   $227.60   $227.60   $227.60  
  Purchase #5 $84.35   13.749%   $95.9473   $95.95   $95.95   $95.90  
  Purchase #6 $213.54   6.239%   $226.8628   $226.86   $226.85   $226.90  
  Purchase #7 $127.90   8.363%   $138.5963   $138.60   $138.60   $138.60  
  7 purchase totals = $915.33       $987.7747   $987.78   $987.75   $987.80