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 $216.99   12.297%   $243.6733   $243.67   $243.65   $243.70  
  Purchase #2 $200.34   8.871%   $218.1122   $218.11   $218.10   $218.10  
  Purchase #3 $234.47   13.615%   $266.3931   $266.39   $266.40   $266.40  
  Purchase #4 $47.95   9.399%   $52.4568   $52.46   $52.45   $52.50  
  Purchase #5 $206.30   6.130%   $218.9462   $218.95   $218.95   $218.90  
  Purchase #6 $234.96   7.854%   $253.4138   $253.41   $253.40   $253.40  
  Purchase #7 $37.28   9.591%   $40.8555   $40.86   $40.85   $40.90  
  7 purchase totals = $1,178.29       $1,293.8509   $1,293.85   $1,293.80   $1,293.90