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 $94.61   13.563%   $107.442   $107.44   $107.45   $107.40  
  Purchase #2 $194.56   9.342%   $212.7358   $212.74   $212.75   $212.70  
  Purchase #3 $68.41   8.143%   $73.9806   $73.98   $74.00   $74.00  
  Purchase #4 $71.74   3.818%   $74.479   $74.48   $74.50   $74.50  
  Purchase #5 $152.88   7.577%   $164.4637   $164.46   $164.45   $164.50  
  Purchase #6 $96.76   12.872%   $109.2149   $109.21   $109.20   $109.20  
  Purchase #7 $219.98   8.233%   $238.091   $238.09   $238.10   $238.10  
  7 purchase totals = $898.94       $980.4070   $980.40   $980.45   $980.40