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 $140.77   7.764%   $151.6994   $151.70   $151.70   $151.70  
  Purchase #2 $117.67   3.827%   $122.1732   $122.17   $122.15   $122.20  
  Purchase #3 $196.40   13.488%   $222.8904   $222.89   $222.90   $222.90  
  Purchase #4 $247.34   8.516%   $268.4035   $268.40   $268.40   $268.40  
  Purchase #5 $93.26   12.700%   $105.104   $105.10   $105.10   $105.10  
  Purchase #6 $218.28   8.222%   $236.227   $236.23   $236.25   $236.20  
  Purchase #7 $188.83   3.758%   $195.9262   $195.93   $195.95   $195.90  
  7 purchase totals = $1,202.55       $1,302.4237   $1,302.42   $1,302.45   $1,302.40