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 $77.34   9.839%   $84.9495   $84.95   $84.95   $84.90  
  Purchase #2 $182.44   7.188%   $195.5538   $195.55   $195.55   $195.60  
  Purchase #3 $217.93   8.717%   $236.927   $236.93   $236.95   $236.90  
  Purchase #4 $244.83   5.337%   $257.8966   $257.90   $257.90   $257.90  
  Purchase #5 $70.50   9.573%   $77.249   $77.25   $77.25   $77.20  
  Purchase #6 $135.67   3.129%   $139.9151   $139.92   $139.90   $139.90  
  Purchase #7 $47.57   5.528%   $50.1997   $50.20   $50.20   $50.20  
  7 purchase totals = $976.28       $1,042.6907   $1,042.70   $1,042.70   $1,042.60