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 $170.67   6.784%   $182.2483   $182.25   $182.25   $182.20  
  Purchase #2 $190.26   5.702%   $201.1086   $201.11   $201.10   $201.10  
  Purchase #3 $50.67   9.684%   $55.5769   $55.58   $55.60   $55.60  
  Purchase #4 $14.42   11.253%   $16.0427   $16.04   $16.05   $16.00  
  Purchase #5 $248.28   9.178%   $271.0671   $271.07   $271.05   $271.10  
  Purchase #6 $120.52   9.551%   $132.0309   $132.03   $132.05   $132.00  
  Purchase #7 $157.34   11.258%   $175.0533   $175.05   $175.05   $175.10  
  7 purchase totals = $952.16       $1,033.1278   $1,033.13   $1,033.15   $1,033.10