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 $204.74   8.538%   $222.2207   $222.22   $222.20   $222.20  
  Purchase #2 $69.97   10.328%   $77.1965   $77.20   $77.20   $77.20  
  Purchase #3 $230.41   9.797%   $252.9833   $252.98   $253.00   $253.00  
  Purchase #4 $119.95   4.709%   $125.5984   $125.60   $125.60   $125.60  
  Purchase #5 $82.72   12.618%   $93.1576   $93.16   $93.15   $93.20  
  Purchase #6 $120.93   6.319%   $128.5716   $128.57   $128.55   $128.60  
  Purchase #7 $110.35   6.564%   $117.5934   $117.59   $117.60   $117.60  
  7 purchase totals = $939.07       $1,017.3215   $1,017.32   $1,017.30   $1,017.40