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 $46.76   9.243%   $51.082   $51.08   $51.10   $51.10  
  Purchase #2 $217.92   11.829%   $243.6978   $243.70   $243.70   $243.70  
  Purchase #3 $91.60   5.331%   $96.4832   $96.48   $96.50   $96.50  
  Purchase #4 $22.89   3.644%   $23.7241   $23.72   $23.70   $23.70  
  Purchase #5 $190.61   4.569%   $199.319   $199.32   $199.30   $199.30  
  Purchase #6 $61.88   3.754%   $64.203   $64.20   $64.20   $64.20  
  Purchase #7 $130.91   4.115%   $136.2969   $136.30   $136.30   $136.30  
  7 purchase totals = $762.57       $814.8060   $814.80   $814.80   $814.80