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 $92.78   3.667%   $96.1822   $96.18   $96.20   $96.20  
  Purchase #2 $243.59   5.723%   $257.5307   $257.53   $257.55   $257.50  
  Purchase #3 $223.75   6.151%   $237.5129   $237.51   $237.50   $237.50  
  Purchase #4 $54.60   8.450%   $59.2137   $59.21   $59.20   $59.20  
  Purchase #5 $215.58   11.264%   $239.8629   $239.86   $239.85   $239.90  
  Purchase #6 $118.70   4.570%   $124.1246   $124.12   $124.10   $124.10  
  Purchase #7 $219.66   13.365%   $249.0176   $249.02   $249.00   $249.00  
  7 purchase totals = $1,168.66       $1,263.4446   $1,263.43   $1,263.40   $1,263.40