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 $192.70   6.165%   $204.58   $204.58   $204.60   $204.60  
  Purchase #2 $248.86   12.424%   $279.7784   $279.78   $279.80   $279.80  
  Purchase #3 $35.28   6.633%   $37.6201   $37.62   $37.60   $37.60  
  Purchase #4 $157.97   11.661%   $176.3909   $176.39   $176.40   $176.40  
  Purchase #5 $37.88   6.131%   $40.2024   $40.20   $40.20   $40.20  
  Purchase #6 $213.90   10.182%   $235.6793   $235.68   $235.70   $235.70  
  Purchase #7 $59.63   7.690%   $64.2155   $64.22   $64.20   $64.20  
  7 purchase totals = $946.22       $1,038.4666   $1,038.47   $1,038.50   $1,038.50