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 $177.43   4.420%   $185.2724   $185.27   $185.25   $185.30  
  Purchase #2 $225.79   6.428%   $240.3038   $240.30   $240.30   $240.30  
  Purchase #3 $21.31   11.301%   $23.7182   $23.72   $23.70   $23.70  
  Purchase #4 $128.65   9.642%   $141.0544   $141.05   $141.05   $141.10  
  Purchase #5 $65.59   3.496%   $67.883   $67.88   $67.90   $67.90  
  Purchase #6 $217.91   10.711%   $241.2503   $241.25   $241.25   $241.30  
  Purchase #7 $87.50   5.166%   $92.0203   $92.02   $92.00   $92.00  
  7 purchase totals = $924.18       $991.5024   $991.49   $991.45   $991.60