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 $78.63   9.405%   $86.0252   $86.03   $86.05   $86.00  
  Purchase #2 $186.44   5.283%   $196.2896   $196.29   $196.30   $196.30  
  Purchase #3 $209.79   5.783%   $221.9222   $221.92   $221.90   $221.90  
  Purchase #4 $196.52   5.282%   $206.9002   $206.90   $206.90   $206.90  
  Purchase #5 $124.98   6.861%   $133.5549   $133.55   $133.55   $133.60  
  Purchase #6 $46.88   5.113%   $49.277   $49.28   $49.30   $49.30  
  Purchase #7 $41.35   11.278%   $46.0135   $46.01   $46.00   $46.00  
  7 purchase totals = $884.59       $939.9826   $939.98   $940.00   $940.00