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 $195.72   6.798%   $209.025   $209.03   $209.05   $209.00  
  Purchase #2 $87.39   5.313%   $92.033   $92.03   $92.05   $92.00  
  Purchase #3 $243.65   13.843%   $277.3785   $277.38   $277.40   $277.40  
  Purchase #4 $86.34   11.332%   $96.124   $96.12   $96.10   $96.10  
  Purchase #5 $87.90   8.352%   $95.2414   $95.24   $95.25   $95.20  
  Purchase #6 $132.80   11.705%   $148.3442   $148.34   $148.35   $148.30  
  Purchase #7 $71.83   8.167%   $77.6964   $77.70   $77.70   $77.70  
  7 purchase totals = $905.63       $995.8425   $995.84   $995.90   $995.70