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 $202.55   11.598%   $226.0417   $226.04   $226.05   $226.00  
  Purchase #2 $239.96   7.227%   $257.3019   $257.30   $257.30   $257.30  
  Purchase #3 $118.43   9.487%   $129.6655   $129.67   $129.65   $129.70  
  Purchase #4 $193.99   11.673%   $216.6345   $216.63   $216.65   $216.60  
  Purchase #5 $238.88   5.562%   $252.1665   $252.17   $252.15   $252.20  
  Purchase #6 $240.40   10.565%   $265.7983   $265.80   $265.80   $265.80  
  Purchase #7 $218.56   7.338%   $234.5979   $234.60   $234.60   $234.60  
  7 purchase totals = $1,452.77       $1,582.2063   $1,582.21   $1,582.20   $1,582.20