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 $34.39   4.759%   $36.0266   $36.03   $36.05   $36.00  
  Purchase #2 $137.97   9.415%   $150.9599   $150.96   $150.95   $151.00  
  Purchase #3 $190.89   13.515%   $216.6888   $216.69   $216.70   $216.70  
  Purchase #4 $47.90   8.242%   $51.8479   $51.85   $51.85   $51.80  
  Purchase #5 $146.42   11.779%   $163.6668   $163.67   $163.65   $163.70  
  Purchase #6 $23.68   9.312%   $25.8851   $25.89   $25.90   $25.90  
  Purchase #7 $84.69   13.791%   $96.3696   $96.37   $96.35   $96.40  
  7 purchase totals = $665.94       $741.4447   $741.46   $741.45   $741.50