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 $216.87   13.320%   $245.7571   $245.76   $245.75   $245.80  
  Purchase #2 $144.90   11.743%   $161.9156   $161.92   $161.90   $161.90  
  Purchase #3 $157.91   7.192%   $169.2669   $169.27   $169.25   $169.30  
  Purchase #4 $55.83   11.642%   $62.3297   $62.33   $62.35   $62.30  
  Purchase #5 $134.86   9.745%   $148.0021   $148.00   $148.00   $148.00  
  Purchase #6 $49.31   13.533%   $55.9831   $55.98   $56.00   $56.00  
  Purchase #7 $24.62   6.682%   $26.2651   $26.27   $26.25   $26.30  
  7 purchase totals = $784.30       $869.5196   $869.53   $869.50   $869.60