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 $153.47   8.187%   $166.0346   $166.03   $166.05   $166.00  
  Purchase #2 $205.98   6.582%   $219.5376   $219.54   $219.55   $219.50  
  Purchase #3 $25.51   10.286%   $28.134   $28.13   $28.15   $28.10  
  Purchase #4 $155.58   4.826%   $163.0883   $163.09   $163.10   $163.10  
  Purchase #5 $76.72   10.283%   $84.6091   $84.61   $84.60   $84.60  
  Purchase #6 $208.28   3.470%   $215.5073   $215.51   $215.50   $215.50  
  Purchase #7 $17.26   7.145%   $18.4932   $18.49   $18.50   $18.50  
  7 purchase totals = $842.80       $895.4041   $895.40   $895.45   $895.30