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 $171.52   13.861%   $195.2944   $195.29   $195.30   $195.30  
  Purchase #2 $93.35   5.512%   $98.4955   $98.50   $98.50   $98.50  
  Purchase #3 $67.73   11.661%   $75.628   $75.63   $75.65   $75.60  
  Purchase #4 $226.28   11.417%   $252.1144   $252.11   $252.10   $252.10  
  Purchase #5 $169.51   8.538%   $183.9828   $183.98   $184.00   $184.00  
  Purchase #6 $250.58   10.735%   $277.4798   $277.48   $277.50   $277.50  
  Purchase #7 $201.97   3.585%   $209.2106   $209.21   $209.20   $209.20  
  7 purchase totals = $1,180.94       $1,292.2055   $1,292.20   $1,292.25   $1,292.20