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 $46.41   5.557%   $48.989   $48.99   $49.00   $49.00  
  Purchase #2 $194.38   11.465%   $216.6657   $216.67   $216.65   $216.70  
  Purchase #3 $53.62   5.808%   $56.7342   $56.73   $56.75   $56.70  
  Purchase #4 $167.88   3.548%   $173.8364   $173.84   $173.85   $173.80  
  Purchase #5 $9.61   10.874%   $10.655   $10.66   $10.65   $10.70  
  Purchase #6 $238.88   13.347%   $270.7633   $270.76   $270.75   $270.80  
  Purchase #7 $103.33   6.550%   $110.0981   $110.10   $110.10   $110.10  
  7 purchase totals = $814.11       $887.7417   $887.75   $887.75   $887.80