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 $237.67   12.414%   $267.1744   $267.17   $267.15   $267.20  
  Purchase #2 $32.85   8.263%   $35.5644   $35.56   $35.55   $35.60  
  Purchase #3 $39.96   11.379%   $44.507   $44.51   $44.50   $44.50  
  Purchase #4 $163.66   8.609%   $177.7495   $177.75   $177.75   $177.70  
  Purchase #5 $181.36   12.138%   $203.3735   $203.37   $203.35   $203.40  
  Purchase #6 $86.88   9.725%   $95.3291   $95.33   $95.35   $95.30  
  Purchase #7 $114.76   12.721%   $129.3586   $129.36   $129.35   $129.40  
  7 purchase totals = $857.14       $953.0565   $953.05   $953.00   $953.10