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 $197.75   12.591%   $222.6487   $222.65   $222.65   $222.60  
  Purchase #2 $205.43   6.294%   $218.3598   $218.36   $218.35   $218.40  
  Purchase #3 $214.43   4.604%   $224.3024   $224.30   $224.30   $224.30  
  Purchase #4 $130.34   6.602%   $138.945   $138.95   $138.95   $138.90  
  Purchase #5 $48.67   4.526%   $50.8728   $50.87   $50.85   $50.90  
  Purchase #6 $5.81   4.378%   $6.0644   $6.06   $6.05   $6.10  
  Purchase #7 $118.98   4.634%   $124.4935   $124.49   $124.50   $124.50  
  7 purchase totals = $921.41       $985.6866   $985.68   $985.65   $985.70