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 $189.79   11.168%   $210.9857   $210.99   $211.00   $211.00  
  Purchase #2 $127.87   4.554%   $133.6932   $133.69   $133.70   $133.70  
  Purchase #3 $224.66   6.274%   $238.7552   $238.76   $238.75   $238.80  
  Purchase #4 $111.58   7.533%   $119.9853   $119.99   $120.00   $120.00  
  Purchase #5 $160.91   10.137%   $177.2214   $177.22   $177.20   $177.20  
  Purchase #6 $48.96   11.295%   $54.49   $54.49   $54.50   $54.50  
  Purchase #7 $125.47   5.411%   $132.2592   $132.26   $132.25   $132.30  
  7 purchase totals = $989.24       $1,067.3900   $1,067.40   $1,067.40   $1,067.50