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 $228.37   8.394%   $247.5394   $247.54   $247.55   $247.50  
  Purchase #2 $247.71   13.314%   $280.6901   $280.69   $280.70   $280.70  
  Purchase #3 $161.61   10.127%   $177.9762   $177.98   $178.00   $178.00  
  Purchase #4 $234.88   10.598%   $259.7726   $259.77   $259.75   $259.80  
  Purchase #5 $153.28   11.229%   $170.4918   $170.49   $170.50   $170.50  
  Purchase #6 $185.93   6.469%   $197.9578   $197.96   $197.95   $198.00  
  Purchase #7 $97.87   4.201%   $101.9815   $101.98   $102.00   $102.00  
  7 purchase totals = $1,309.65       $1,436.4094   $1,436.41   $1,436.45   $1,436.50