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 $59.90   3.168%   $61.7976   $61.80   $61.80   $61.80  
  Purchase #2 $133.97   11.752%   $149.7142   $149.71   $149.70   $149.70  
  Purchase #3 $36.38   8.268%   $39.3879   $39.39   $39.40   $39.40  
  Purchase #4 $189.84   4.175%   $197.7658   $197.77   $197.75   $197.80  
  Purchase #5 $127.67   6.384%   $135.8205   $135.82   $135.80   $135.80  
  Purchase #6 $29.52   8.559%   $32.0466   $32.05   $32.05   $32.00  
  Purchase #7 $127.48   10.590%   $140.9801   $140.98   $141.00   $141.00  
  7 purchase totals = $704.76       $757.5127   $757.52   $757.50   $757.50