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 $243.96   11.186%   $271.2494   $271.25   $271.25   $271.20  
  Purchase #2 $93.65   13.703%   $106.4829   $106.48   $106.50   $106.50  
  Purchase #3 $197.92   3.796%   $205.433   $205.43   $205.45   $205.40  
  Purchase #4 $35.25   13.154%   $39.8868   $39.89   $39.90   $39.90  
  Purchase #5 $200.54   5.550%   $211.67   $211.67   $211.65   $211.70  
  Purchase #6 $132.99   6.607%   $141.7766   $141.78   $141.80   $141.80  
  Purchase #7 $14.77   13.637%   $16.7842   $16.78   $16.80   $16.80  
  7 purchase totals = $919.08       $993.2829   $993.28   $993.35   $993.30