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 $167.68   10.656%   $185.548   $185.55   $185.55   $185.50  
  Purchase #2 $121.42   7.643%   $130.7001   $130.70   $130.70   $130.70  
  Purchase #3 $93.65   11.576%   $104.4909   $104.49   $104.50   $104.50  
  Purchase #4 $59.86   10.373%   $66.0693   $66.07   $66.05   $66.10  
  Purchase #5 $43.74   7.191%   $46.8853   $46.89   $46.90   $46.90  
  Purchase #6 $195.83   3.375%   $202.4393   $202.44   $202.45   $202.40  
  Purchase #7 $173.73   7.470%   $186.7076   $186.71   $186.70   $186.70  
  7 purchase totals = $855.91       $922.8405   $922.85   $922.85   $922.80