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 $85.66   9.604%   $93.8868   $93.89   $93.90   $93.90  
  Purchase #2 $218.68   7.796%   $235.7283   $235.73   $235.75   $235.70  
  Purchase #3 $24.80   7.703%   $26.7103   $26.71   $26.70   $26.70  
  Purchase #4 $236.98   7.811%   $255.4905   $255.49   $255.50   $255.50  
  Purchase #5 $85.78   7.804%   $92.4743   $92.47   $92.45   $92.50  
  Purchase #6 $41.55   8.535%   $45.0963   $45.10   $45.10   $45.10  
  Purchase #7 $154.52   10.585%   $170.8759   $170.88   $170.90   $170.90  
  7 purchase totals = $847.97       $920.2624   $920.27   $920.30   $920.30