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 $232.59   10.827%   $257.7725   $257.77   $257.75   $257.80  
  Purchase #2 $118.42   7.734%   $127.5786   $127.58   $127.60   $127.60  
  Purchase #3 $203.75   12.539%   $229.2982   $229.30   $229.30   $229.30  
  Purchase #4 $86.84   8.872%   $94.5444   $94.54   $94.55   $94.50  
  Purchase #5 $22.76   9.740%   $24.9768   $24.98   $25.00   $25.00  
  Purchase #6 $237.86   5.447%   $250.8162   $250.82   $250.80   $250.80  
  Purchase #7 $222.87   8.262%   $241.2835   $241.28   $241.30   $241.30  
  7 purchase totals = $1,125.09       $1,226.2702   $1,226.27   $1,226.30   $1,226.30