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 $228.69   12.161%   $256.501   $256.50   $256.50   $256.50  
  Purchase #2 $160.98   9.680%   $176.5629   $176.56   $176.55   $176.60  
  Purchase #3 $98.65   5.201%   $103.7808   $103.78   $103.80   $103.80  
  Purchase #4 $76.74   11.233%   $85.3602   $85.36   $85.35   $85.40  
  Purchase #5 $161.99   13.559%   $183.9542   $183.95   $183.95   $184.00  
  Purchase #6 $189.95   4.379%   $198.2679   $198.27   $198.25   $198.30  
  Purchase #7 $105.79   12.224%   $118.7218   $118.72   $118.70   $118.70  
  7 purchase totals = $1,022.79       $1,123.1488   $1,123.14   $1,123.10   $1,123.30