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 $241.61   9.692%   $265.0268   $265.03   $265.05   $265.00  
  Purchase #2 $58.79   9.868%   $64.5914   $64.59   $64.60   $64.60  
  Purchase #3 $130.82   7.569%   $140.7218   $140.72   $140.70   $140.70  
  Purchase #4 $53.58   8.343%   $58.0502   $58.05   $58.05   $58.10  
  Purchase #5 $103.64   7.199%   $111.101   $111.10   $111.10   $111.10  
  Purchase #6 $164.46   8.237%   $178.0066   $178.01   $178.00   $178.00  
  Purchase #7 $107.95   8.520%   $117.1473   $117.15   $117.15   $117.10  
  7 purchase totals = $860.85       $934.6451   $934.65   $934.65   $934.60