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 $86.60   11.313%   $96.3971   $96.40   $96.40   $96.40  
  Purchase #2 $103.46   9.747%   $113.5442   $113.54   $113.55   $113.50  
  Purchase #3 $42.85   6.325%   $45.5603   $45.56   $45.55   $45.60  
  Purchase #4 $180.99   6.490%   $192.7363   $192.74   $192.75   $192.70  
  Purchase #5 $93.44   6.797%   $99.7911   $99.79   $99.80   $99.80  
  Purchase #6 $195.78   6.476%   $208.4587   $208.46   $208.45   $208.50  
  Purchase #7 $88.62   8.775%   $96.3964   $96.40   $96.40   $96.40  
  7 purchase totals = $791.74       $852.8841   $852.89   $852.90   $852.90