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 $33.57   5.695%   $35.4818   $35.48   $35.50   $35.50  
  Purchase #2 $61.50   7.741%   $66.2607   $66.26   $66.25   $66.30  
  Purchase #3 $164.73   9.675%   $180.6676   $180.67   $180.65   $180.70  
  Purchase #4 $223.70   9.855%   $245.7456   $245.75   $245.75   $245.70  
  Purchase #5 $184.52   11.384%   $205.5258   $205.53   $205.55   $205.50  
  Purchase #6 $96.98   5.787%   $102.5922   $102.59   $102.60   $102.60  
  Purchase #7 $96.61   5.292%   $101.7226   $101.72   $101.70   $101.70  
  7 purchase totals = $861.61       $937.9963   $938.00   $938.00   $938.00