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 $69.73   5.195%   $73.3525   $73.35   $73.35   $73.40  
  Purchase #2 $237.87   11.306%   $264.7636   $264.76   $264.75   $264.80  
  Purchase #3 $165.63   7.581%   $178.1864   $178.19   $178.20   $178.20  
  Purchase #4 $91.81   3.725%   $95.2299   $95.23   $95.25   $95.20  
  Purchase #5 $18.51   11.563%   $20.6503   $20.65   $20.65   $20.70  
  Purchase #6 $228.62   9.753%   $250.9173   $250.92   $250.90   $250.90  
  Purchase #7 $66.52   4.371%   $69.4276   $69.43   $69.45   $69.40  
  7 purchase totals = $878.69       $952.5276   $952.53   $952.55   $952.60