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 $241.66   10.591%   $267.2542   $267.25   $267.25   $267.30  
  Purchase #2 $194.75   8.546%   $211.3933   $211.39   $211.40   $211.40  
  Purchase #3 $178.73   11.376%   $199.0623   $199.06   $199.05   $199.10  
  Purchase #4 $160.64   8.317%   $174.0004   $174.00   $174.00   $174.00  
  Purchase #5 $27.53   11.166%   $30.604   $30.60   $30.60   $30.60  
  Purchase #6 $64.77   6.829%   $69.1931   $69.19   $69.20   $69.20  
  Purchase #7 $25.96   6.403%   $27.6222   $27.62   $27.60   $27.60  
  7 purchase totals = $894.04       $979.1295   $979.11   $979.10   $979.20