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 $5.35   8.616%   $5.811   $5.81   $5.80   $5.80  
  Purchase #2 $19.99   4.383%   $20.8662   $20.87   $20.85   $20.90  
  Purchase #3 $177.60   7.553%   $191.0141   $191.01   $191.00   $191.00  
  Purchase #4 $77.49   13.280%   $87.7807   $87.78   $87.80   $87.80  
  Purchase #5 $203.94   3.221%   $210.5089   $210.51   $210.50   $210.50  
  Purchase #6 $77.31   6.700%   $82.4898   $82.49   $82.50   $82.50  
  Purchase #7 $125.73   9.792%   $138.0415   $138.04   $138.05   $138.00  
  7 purchase totals = $687.41       $736.5122   $736.51   $736.50   $736.50