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 $176.97   12.781%   $199.5885   $199.59   $199.60   $199.60  
  Purchase #2 $120.32   8.405%   $130.4329   $130.43   $130.45   $130.40  
  Purchase #3 $138.25   3.463%   $143.0376   $143.04   $143.05   $143.00  
  Purchase #4 $40.75   6.223%   $43.2859   $43.29   $43.30   $43.30  
  Purchase #5 $245.43   9.392%   $268.4808   $268.48   $268.50   $268.50  
  Purchase #6 $250.51   9.664%   $274.7193   $274.72   $274.70   $274.70  
  Purchase #7 $193.56   5.220%   $203.6638   $203.66   $203.65   $203.70  
  7 purchase totals = $1,165.79       $1,263.2088   $1,263.21   $1,263.25   $1,263.20