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 $93.35   3.140%   $96.2812   $96.28   $96.30   $96.30  
  Purchase #2 $189.77   3.112%   $195.6756   $195.68   $195.70   $195.70  
  Purchase #3 $136.83   5.759%   $144.71   $144.71   $144.70   $144.70  
  Purchase #4 $101.79   8.823%   $110.7709   $110.77   $110.75   $110.80  
  Purchase #5 $226.63   12.309%   $254.5259   $254.53   $254.55   $254.50  
  Purchase #6 $32.52   5.691%   $34.3707   $34.37   $34.35   $34.40  
  Purchase #7 $106.46   12.220%   $119.4694   $119.47   $119.45   $119.50  
  7 purchase totals = $887.35       $955.8037   $955.81   $955.80   $955.90