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 $164.87   11.641%   $184.0625   $184.06   $184.05   $184.10  
  Purchase #2 $241.26   13.424%   $273.6467   $273.65   $273.65   $273.60  
  Purchase #3 $233.41   9.469%   $255.5116   $255.51   $255.50   $255.50  
  Purchase #4 $162.56   11.266%   $180.874   $180.87   $180.85   $180.90  
  Purchase #5 $105.38   13.238%   $119.3302   $119.33   $119.35   $119.30  
  Purchase #6 $55.60   5.451%   $58.6308   $58.63   $58.65   $58.60  
  Purchase #7 $152.36   5.436%   $160.6423   $160.64   $160.65   $160.60  
  7 purchase totals = $1,115.44       $1,232.6981   $1,232.69   $1,232.70   $1,232.60