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 $69.28   6.380%   $73.7001   $73.70   $73.70   $73.70  
  Purchase #2 $112.65   3.430%   $116.5139   $116.51   $116.50   $116.50  
  Purchase #3 $88.85   5.775%   $93.9811   $93.98   $94.00   $94.00  
  Purchase #4 $151.43   6.441%   $161.1836   $161.18   $161.20   $161.20  
  Purchase #5 $49.65   7.825%   $53.5351   $53.54   $53.55   $53.50  
  Purchase #6 $246.41   11.597%   $274.9862   $274.99   $275.00   $275.00  
  Purchase #7 $203.27   6.297%   $216.0699   $216.07   $216.05   $216.10  
  7 purchase totals = $921.54       $989.9699   $989.97   $990.00   $990.00