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 $65.61   12.224%   $73.6302   $73.63   $73.65   $73.60  
  Purchase #2 $32.96   9.560%   $36.111   $36.11   $36.10   $36.10  
  Purchase #3 $71.87   12.731%   $81.0198   $81.02   $81.00   $81.00  
  Purchase #4 $95.54   9.178%   $104.3087   $104.31   $104.30   $104.30  
  Purchase #5 $86.97   10.853%   $96.4089   $96.41   $96.40   $96.40  
  Purchase #6 $203.70   10.512%   $225.1129   $225.11   $225.10   $225.10  
  Purchase #7 $62.40   13.481%   $70.8121   $70.81   $70.80   $70.80  
  7 purchase totals = $619.05       $687.4036   $687.40   $687.35   $687.30