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 $246.36   8.676%   $267.7342   $267.73   $267.75   $267.70  
  Purchase #2 $33.42   9.735%   $36.6734   $36.67   $36.65   $36.70  
  Purchase #3 $90.30   3.497%   $93.4578   $93.46   $93.45   $93.50  
  Purchase #4 $241.77   9.138%   $263.8629   $263.86   $263.85   $263.90  
  Purchase #5 $222.31   12.690%   $250.5211   $250.52   $250.50   $250.50  
  Purchase #6 $87.28   12.857%   $98.5016   $98.50   $98.50   $98.50  
  Purchase #7 $217.54   11.223%   $241.9545   $241.95   $241.95   $242.00  
  7 purchase totals = $1,138.98       $1,252.7055   $1,252.69   $1,252.65   $1,252.80