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 $246.54   6.701%   $263.0606   $263.06   $263.05   $263.10  
  Purchase #2 $129.39   10.264%   $142.6706   $142.67   $142.65   $142.70  
  Purchase #3 $228.74   10.780%   $253.3982   $253.40   $253.40   $253.40  
  Purchase #4 $117.77   9.289%   $128.7097   $128.71   $128.70   $128.70  
  Purchase #5 $75.66   12.848%   $85.3808   $85.38   $85.40   $85.40  
  Purchase #6 $250.75   5.749%   $265.1656   $265.17   $265.15   $265.20  
  Purchase #7 $194.73   11.822%   $217.751   $217.75   $217.75   $217.80  
  7 purchase totals = $1,243.58       $1,356.1365   $1,356.14   $1,356.10   $1,356.30