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 $233.25   3.546%   $241.521   $241.52   $241.50   $241.50  
  Purchase #2 $212.81   11.536%   $237.3598   $237.36   $237.35   $237.40  
  Purchase #3 $55.88   10.457%   $61.7234   $61.72   $61.70   $61.70  
  Purchase #4 $188.30   11.178%   $209.3482   $209.35   $209.35   $209.30  
  Purchase #5 $242.25   10.413%   $267.4755   $267.48   $267.50   $267.50  
  Purchase #6 $204.51   10.463%   $225.9079   $225.91   $225.90   $225.90  
  Purchase #7 $122.40   6.448%   $130.2924   $130.29   $130.30   $130.30  
  7 purchase totals = $1,259.40       $1,373.6282   $1,373.63   $1,373.60   $1,373.60