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 $201.93   11.801%   $225.7598   $225.76   $225.75   $225.80  
  Purchase #2 $88.36   7.483%   $94.972   $94.97   $94.95   $95.00  
  Purchase #3 $29.77   11.599%   $33.223   $33.22   $33.20   $33.20  
  Purchase #4 $214.95   9.525%   $235.424   $235.42   $235.40   $235.40  
  Purchase #5 $15.48   13.838%   $17.6221   $17.62   $17.60   $17.60  
  Purchase #6 $239.87   13.557%   $272.3892   $272.39   $272.40   $272.40  
  Purchase #7 $125.35   5.171%   $131.8318   $131.83   $131.85   $131.80  
  7 purchase totals = $915.71       $1,011.2219   $1,011.21   $1,011.15   $1,011.20