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 $92.97   12.824%   $104.8925   $104.89   $104.90   $104.90  
  Purchase #2 $68.87   11.376%   $76.7047   $76.70   $76.70   $76.70  
  Purchase #3 $137.95   11.599%   $153.9508   $153.95   $153.95   $154.00  
  Purchase #4 $244.84   13.347%   $277.5188   $277.52   $277.50   $277.50  
  Purchase #5 $43.50   7.523%   $46.7725   $46.77   $46.75   $46.80  
  Purchase #6 $162.51   5.373%   $171.2417   $171.24   $171.25   $171.20  
  Purchase #7 $224.88   3.441%   $232.6181   $232.62   $232.60   $232.60  
  7 purchase totals = $975.52       $1,063.6991   $1,063.69   $1,063.65   $1,063.70