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 $224.28   8.130%   $242.514   $242.51   $242.50   $242.50  
  Purchase #2 $58.86   11.609%   $65.6931   $65.69   $65.70   $65.70  
  Purchase #3 $58.60   6.188%   $62.2262   $62.23   $62.25   $62.20  
  Purchase #4 $125.81   6.579%   $134.087   $134.09   $134.10   $134.10  
  Purchase #5 $65.91   10.303%   $72.7007   $72.70   $72.70   $72.70  
  Purchase #6 $70.65   9.110%   $77.0862   $77.09   $77.10   $77.10  
  Purchase #7 $126.86   9.227%   $138.5654   $138.57   $138.55   $138.60  
  7 purchase totals = $730.97       $792.8726   $792.88   $792.90   $792.90