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 $196.87   8.223%   $213.0586   $213.06   $213.05   $213.10  
  Purchase #2 $169.80   10.430%   $187.5101   $187.51   $187.50   $187.50  
  Purchase #3 $109.90   12.491%   $123.6276   $123.63   $123.65   $123.60  
  Purchase #4 $106.53   5.137%   $112.0024   $112.00   $112.00   $112.00  
  Purchase #5 $139.53   3.134%   $143.9029   $143.90   $143.90   $143.90  
  Purchase #6 $160.28   12.692%   $180.6227   $180.62   $180.60   $180.60  
  Purchase #7 $66.37   4.857%   $69.5936   $69.59   $69.60   $69.60  
  7 purchase totals = $949.28       $1,030.3179   $1,030.31   $1,030.30   $1,030.30