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 $49.38   6.629%   $52.6534   $52.65   $52.65   $52.70  
  Purchase #2 $119.84   11.303%   $133.3855   $133.39   $133.40   $133.40  
  Purchase #3 $92.60   10.125%   $101.9758   $101.98   $102.00   $102.00  
  Purchase #4 $221.61   9.472%   $242.6009   $242.60   $242.60   $242.60  
  Purchase #5 $26.52   11.709%   $29.6252   $29.63   $29.65   $29.60  
  Purchase #6 $100.91   10.307%   $111.3108   $111.31   $111.30   $111.30  
  Purchase #7 $36.79   7.214%   $39.444   $39.44   $39.45   $39.40  
  7 purchase totals = $647.65       $710.9956   $711.00   $711.05   $711.00