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 $84.27   8.797%   $91.6832   $91.68   $91.70   $91.70  
  Purchase #2 $233.37   13.583%   $265.0686   $265.07   $265.05   $265.10  
  Purchase #3 $120.53   12.874%   $136.047   $136.05   $136.05   $136.00  
  Purchase #4 $5.99   10.865%   $6.6408   $6.64   $6.65   $6.60  
  Purchase #5 $227.60   3.535%   $235.6457   $235.65   $235.65   $235.60  
  Purchase #6 $46.31   3.133%   $47.7609   $47.76   $47.75   $47.80  
  Purchase #7 $192.84   5.776%   $203.9784   $203.98   $204.00   $204.00  
  7 purchase totals = $910.91       $986.8246   $986.83   $986.85   $986.80