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 $88.27   9.389%   $96.5577   $96.56   $96.55   $96.60  
  Purchase #2 $44.62   8.375%   $48.3569   $48.36   $48.35   $48.40  
  Purchase #3 $80.26   6.739%   $85.6687   $85.67   $85.65   $85.70  
  Purchase #4 $206.89   4.397%   $215.987   $215.99   $216.00   $216.00  
  Purchase #5 $132.65   13.383%   $150.4025   $150.40   $150.40   $150.40  
  Purchase #6 $117.87   7.351%   $126.5346   $126.53   $126.55   $126.50  
  Purchase #7 $134.47   6.711%   $143.4943   $143.49   $143.50   $143.50  
  7 purchase totals = $805.03       $867.0017   $867.00   $867.00   $867.10