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 $197.65   4.210%   $205.9711   $205.97   $205.95   $206.00  
  Purchase #2 $81.96   12.757%   $92.4156   $92.42   $92.40   $92.40  
  Purchase #3 $78.90   8.440%   $85.5592   $85.56   $85.55   $85.60  
  Purchase #4 $184.38   11.532%   $205.6427   $205.64   $205.65   $205.60  
  Purchase #5 $59.48   9.840%   $65.3328   $65.33   $65.35   $65.30  
  Purchase #6 $190.65   8.839%   $207.5016   $207.50   $207.50   $207.50  
  Purchase #7 $80.86   10.850%   $89.6333   $89.63   $89.65   $89.60  
  7 purchase totals = $873.88       $952.0563   $952.05   $952.05   $952.00