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 $58.45   12.845%   $65.9579   $65.96   $65.95   $66.00  
  Purchase #2 $111.84   5.780%   $118.3044   $118.30   $118.30   $118.30  
  Purchase #3 $76.62   8.205%   $82.9067   $82.91   $82.90   $82.90  
  Purchase #4 $229.78   5.573%   $242.5856   $242.59   $242.60   $242.60  
  Purchase #5 $92.67   12.326%   $104.0925   $104.09   $104.10   $104.10  
  Purchase #6 $103.75   9.211%   $113.3064   $113.31   $113.30   $113.30  
  Purchase #7 $66.74   13.406%   $75.6872   $75.69   $75.70   $75.70  
  7 purchase totals = $739.85       $802.8407   $802.85   $802.85   $802.90