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 $67.43   9.448%   $73.8008   $73.80   $73.80   $73.80  
  Purchase #2 $116.56   12.302%   $130.8992   $130.90   $130.90   $130.90  
  Purchase #3 $34.76   10.130%   $38.2812   $38.28   $38.30   $38.30  
  Purchase #4 $227.91   10.450%   $251.7266   $251.73   $251.75   $251.70  
  Purchase #5 $142.47   13.404%   $161.5667   $161.57   $161.55   $161.60  
  Purchase #6 $45.81   8.766%   $49.8257   $49.83   $49.85   $49.80  
  Purchase #7 $23.88   8.681%   $25.953   $25.95   $25.95   $26.00  
  7 purchase totals = $658.82       $732.0532   $732.06   $732.10   $732.10