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 $160.53   10.717%   $177.734   $177.73   $177.75   $177.70  
  Purchase #2 $73.48   3.391%   $75.9717   $75.97   $75.95   $76.00  
  Purchase #3 $48.36   10.203%   $53.2942   $53.29   $53.30   $53.30  
  Purchase #4 $218.94   8.117%   $236.7114   $236.71   $236.70   $236.70  
  Purchase #5 $86.40   12.617%   $97.3011   $97.30   $97.30   $97.30  
  Purchase #6 $113.67   13.173%   $128.6437   $128.64   $128.65   $128.60  
  Purchase #7 $212.86   13.498%   $241.5918   $241.59   $241.60   $241.60  
  7 purchase totals = $914.24       $1,011.2479   $1,011.23   $1,011.25   $1,011.20