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 $209.52   6.626%   $223.4028   $223.40   $223.40   $223.40  
  Purchase #2 $246.32   8.538%   $267.3508   $267.35   $267.35   $267.40  
  Purchase #3 $70.71   7.718%   $76.1674   $76.17   $76.15   $76.20  
  Purchase #4 $125.76   12.631%   $141.6447   $141.64   $141.65   $141.60  
  Purchase #5 $81.92   5.502%   $86.4272   $86.43   $86.45   $86.40  
  Purchase #6 $97.80   8.449%   $106.0631   $106.06   $106.05   $106.10  
  Purchase #7 $77.42   6.541%   $82.484   $82.48   $82.50   $82.50  
  7 purchase totals = $909.45       $983.5400   $983.53   $983.55   $983.60