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 $88.27   11.857%   $98.7362   $98.74   $98.75   $98.70  
  Purchase #2 $27.70   5.854%   $29.3216   $29.32   $29.30   $29.30  
  Purchase #3 $167.32   3.310%   $172.8583   $172.86   $172.85   $172.90  
  Purchase #4 $81.40   11.731%   $90.949   $90.95   $90.95   $90.90  
  Purchase #5 $16.96   6.544%   $18.0699   $18.07   $18.05   $18.10  
  Purchase #6 $205.39   6.817%   $219.3914   $219.39   $219.40   $219.40  
  Purchase #7 $215.41   11.358%   $239.8763   $239.88   $239.90   $239.90  
  7 purchase totals = $802.45       $869.2027   $869.21   $869.20   $869.20