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 $234.46   5.286%   $246.8536   $246.85   $246.85   $246.90  
  Purchase #2 $54.88   11.521%   $61.2027   $61.20   $61.20   $61.20  
  Purchase #3 $102.68   5.587%   $108.4167   $108.42   $108.40   $108.40  
  Purchase #4 $85.51   4.846%   $89.6538   $89.65   $89.65   $89.70  
  Purchase #5 $19.59   13.392%   $22.2135   $22.21   $22.20   $22.20  
  Purchase #6 $224.37   4.738%   $235.0007   $235.00   $235.00   $235.00  
  Purchase #7 $22.98   7.443%   $24.6904   $24.69   $24.70   $24.70  
  7 purchase totals = $744.47       $788.0314   $788.02   $788.00   $788.10