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 $233.72   13.555%   $265.4007   $265.40   $265.40   $265.40  
  Purchase #2 $54.63   13.473%   $61.9903   $61.99   $62.00   $62.00  
  Purchase #3 $117.44   13.484%   $133.2756   $133.28   $133.30   $133.30  
  Purchase #4 $239.64   3.204%   $247.3181   $247.32   $247.30   $247.30  
  Purchase #5 $174.47   5.401%   $183.8931   $183.89   $183.90   $183.90  
  Purchase #6 $180.44   12.771%   $203.484   $203.48   $203.50   $203.50  
  Purchase #7 $187.94   5.386%   $198.0624   $198.06   $198.05   $198.10  
  7 purchase totals = $1,188.28       $1,293.4242   $1,293.42   $1,293.45   $1,293.50