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 $202.35   11.440%   $225.4988   $225.50   $225.50   $225.50  
  Purchase #2 $146.62   9.569%   $160.6501   $160.65   $160.65   $160.70  
  Purchase #3 $84.28   7.525%   $90.6221   $90.62   $90.60   $90.60  
  Purchase #4 $247.91   4.565%   $259.2271   $259.23   $259.25   $259.20  
  Purchase #5 $230.85   7.424%   $247.9883   $247.99   $248.00   $248.00  
  Purchase #6 $105.83   9.482%   $115.8648   $115.86   $115.85   $115.90  
  Purchase #7 $83.27   13.145%   $94.2158   $94.22   $94.20   $94.20  
  7 purchase totals = $1,101.11       $1,194.0670   $1,194.07   $1,194.05   $1,194.10