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 $65.92   12.632%   $74.247   $74.25   $74.25   $74.20  
  Purchase #2 $9.67   6.566%   $10.3049   $10.30   $10.30   $10.30  
  Purchase #3 $240.47   4.104%   $250.3389   $250.34   $250.35   $250.30  
  Purchase #4 $110.54   11.675%   $123.4455   $123.45   $123.45   $123.40  
  Purchase #5 $157.69   8.230%   $170.6679   $170.67   $170.65   $170.70  
  Purchase #6 $201.64   5.520%   $212.7705   $212.77   $212.75   $212.80  
  Purchase #7 $154.37   3.238%   $159.3685   $159.37   $159.35   $159.40  
  7 purchase totals = $940.30       $1,001.1432   $1,001.15   $1,001.10   $1,001.10