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 $107.34   5.671%   $113.4273   $113.43   $113.45   $113.40  
  Purchase #2 $166.36   4.269%   $173.4619   $173.46   $173.45   $173.50  
  Purchase #3 $77.90   5.771%   $82.3956   $82.40   $82.40   $82.40  
  Purchase #4 $43.93   12.789%   $49.5482   $49.55   $49.55   $49.50  
  Purchase #5 $219.97   5.198%   $231.404   $231.40   $231.40   $231.40  
  Purchase #6 $87.68   5.235%   $92.27   $92.27   $92.25   $92.30  
  Purchase #7 $88.75   5.357%   $93.5043   $93.50   $93.50   $93.50  
  7 purchase totals = $791.93       $836.0113   $836.01   $836.00   $836.00