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 $70.65   8.288%   $76.5055   $76.51   $76.50   $76.50  
  Purchase #2 $84.63   8.659%   $91.9581   $91.96   $91.95   $92.00  
  Purchase #3 $157.77   3.646%   $163.5223   $163.52   $163.50   $163.50  
  Purchase #4 $126.72   8.694%   $137.737   $137.74   $137.75   $137.70  
  Purchase #5 $42.51   3.304%   $43.9145   $43.91   $43.90   $43.90  
  Purchase #6 $212.93   8.681%   $231.4145   $231.41   $231.40   $231.40  
  Purchase #7 $53.63   5.813%   $56.7475   $56.75   $56.75   $56.70  
  7 purchase totals = $748.84       $801.7994   $801.80   $801.75   $801.70