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 $212.49   5.499%   $224.1748   $224.17   $224.15   $224.20  
  Purchase #2 $125.41   11.299%   $139.5801   $139.58   $139.60   $139.60  
  Purchase #3 $137.93   11.198%   $153.3754   $153.38   $153.40   $153.40  
  Purchase #4 $121.82   4.397%   $127.1764   $127.18   $127.20   $127.20  
  Purchase #5 $248.56   9.412%   $271.9545   $271.95   $271.95   $272.00  
  Purchase #6 $113.44   5.270%   $119.4183   $119.42   $119.40   $119.40  
  Purchase #7 $22.76   8.413%   $24.6748   $24.67   $24.65   $24.70  
  7 purchase totals = $982.41       $1,060.3543   $1,060.35   $1,060.35   $1,060.50