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 $154.44   13.438%   $175.1936   $175.19   $175.20   $175.20  
  Purchase #2 $60.70   3.366%   $62.7432   $62.74   $62.75   $62.70  
  Purchase #3 $205.47   11.121%   $228.3203   $228.32   $228.30   $228.30  
  Purchase #4 $214.53   12.536%   $241.4235   $241.42   $241.40   $241.40  
  Purchase #5 $20.42   13.605%   $23.1981   $23.20   $23.20   $23.20  
  Purchase #6 $53.82   12.467%   $60.5297   $60.53   $60.55   $60.50  
  Purchase #7 $222.28   8.417%   $240.9893   $240.99   $241.00   $241.00  
  7 purchase totals = $931.66       $1,032.3977   $1,032.39   $1,032.40   $1,032.30