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 $217.64   13.367%   $246.7319   $246.73   $246.75   $246.70  
  Purchase #2 $179.30   9.471%   $196.2815   $196.28   $196.30   $196.30  
  Purchase #3 $107.80   9.733%   $118.2922   $118.29   $118.30   $118.30  
  Purchase #4 $68.29   11.247%   $75.9706   $75.97   $75.95   $76.00  
  Purchase #5 $52.71   3.240%   $54.4178   $54.42   $54.40   $54.40  
  Purchase #6 $116.68   13.301%   $132.1996   $132.20   $132.20   $132.20  
  Purchase #7 $234.37   13.531%   $266.0826   $266.08   $266.10   $266.10  
  7 purchase totals = $976.79       $1,089.9762   $1,089.97   $1,090.00   $1,090.00