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 $57.92   8.650%   $62.9301   $62.93   $62.95   $62.90  
  Purchase #2 $24.38   10.839%   $27.0225   $27.02   $27.00   $27.00  
  Purchase #3 $15.90   11.526%   $17.7326   $17.73   $17.75   $17.70  
  Purchase #4 $36.67   12.544%   $41.2699   $41.27   $41.25   $41.30  
  Purchase #5 $206.65   10.738%   $228.8401   $228.84   $228.85   $228.80  
  Purchase #6 $241.47   12.789%   $272.3516   $272.35   $272.35   $272.40  
  Purchase #7 $78.97   13.604%   $89.7131   $89.71   $89.70   $89.70  
  7 purchase totals = $661.96       $739.8599   $739.85   $739.85   $739.80