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 $59.96   13.472%   $68.0378   $68.04   $68.05   $68.00  
  Purchase #2 $95.49   11.505%   $106.4761   $106.48   $106.50   $106.50  
  Purchase #3 $12.93   5.747%   $13.6731   $13.67   $13.65   $13.70  
  Purchase #4 $241.66   12.733%   $272.4306   $272.43   $272.45   $272.40  
  Purchase #5 $217.28   13.553%   $246.728   $246.73   $246.75   $246.70  
  Purchase #6 $185.92   8.298%   $201.3476   $201.35   $201.35   $201.30  
  Purchase #7 $105.75   10.812%   $117.1837   $117.18   $117.20   $117.20  
  7 purchase totals = $918.99       $1,025.8769   $1,025.88   $1,025.95   $1,025.80