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 $40.54   6.149%   $43.0328   $43.03   $43.05   $43.00  
  Purchase #2 $114.62   4.210%   $119.4455   $119.45   $119.45   $119.40  
  Purchase #3 $154.69   13.409%   $175.4324   $175.43   $175.45   $175.40  
  Purchase #4 $209.67   12.454%   $235.7823   $235.78   $235.80   $235.80  
  Purchase #5 $157.29   3.347%   $162.5545   $162.55   $162.55   $162.60  
  Purchase #6 $176.59   5.455%   $186.223   $186.22   $186.20   $186.20  
  Purchase #7 $102.48   5.353%   $107.9658   $107.97   $107.95   $108.00  
  7 purchase totals = $955.88       $1,030.4363   $1,030.43   $1,030.45   $1,030.40