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 $117.45   13.685%   $133.523   $133.52   $133.50   $133.50  
  Purchase #2 $59.83   4.659%   $62.6175   $62.62   $62.60   $62.60  
  Purchase #3 $7.92   3.302%   $8.1815   $8.18   $8.20   $8.20  
  Purchase #4 $243.76   12.321%   $273.7937   $273.79   $273.80   $273.80  
  Purchase #5 $228.56   12.560%   $257.2671   $257.27   $257.25   $257.30  
  Purchase #6 $204.68   4.543%   $213.9786   $213.98   $214.00   $214.00  
  Purchase #7 $233.58   8.536%   $253.5184   $253.52   $253.50   $253.50  
  7 purchase totals = $1,095.78       $1,202.8798   $1,202.88   $1,202.85   $1,202.90