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 $233.54   11.454%   $260.2897   $260.29   $260.30   $260.30  
  Purchase #2 $184.40   13.611%   $209.4987   $209.50   $209.50   $209.50  
  Purchase #3 $87.25   6.135%   $92.6028   $92.60   $92.60   $92.60  
  Purchase #4 $88.47   5.770%   $93.5747   $93.57   $93.55   $93.60  
  Purchase #5 $130.96   5.538%   $138.2126   $138.21   $138.20   $138.20  
  Purchase #6 $52.95   12.860%   $59.7594   $59.76   $59.75   $59.80  
  Purchase #7 $83.42   4.402%   $87.0921   $87.09   $87.10   $87.10  
  7 purchase totals = $860.99       $941.0300   $941.02   $941.00   $941.10