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 $87.58   6.873%   $93.5994   $93.60   $93.60   $93.60  
  Purchase #2 $44.92   5.645%   $47.4557   $47.46   $47.45   $47.50  
  Purchase #3 $5.54   10.601%   $6.1273   $6.13   $6.15   $6.10  
  Purchase #4 $184.80   3.346%   $190.9834   $190.98   $191.00   $191.00  
  Purchase #5 $224.31   10.302%   $247.4184   $247.42   $247.40   $247.40  
  Purchase #6 $113.67   9.130%   $124.0481   $124.05   $124.05   $124.00  
  Purchase #7 $77.92   13.417%   $88.3745   $88.37   $88.35   $88.40  
  7 purchase totals = $738.74       $798.0068   $798.01   $798.00   $798.00