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 $92.38   13.817%   $105.1441   $105.14   $105.15   $105.10  
  Purchase #2 $207.69   12.635%   $233.9316   $233.93   $233.95   $233.90  
  Purchase #3 $99.32   11.297%   $110.5402   $110.54   $110.55   $110.50  
  Purchase #4 $205.47   9.428%   $224.8417   $224.84   $224.85   $224.80  
  Purchase #5 $235.30   3.178%   $242.7778   $242.78   $242.80   $242.80  
  Purchase #6 $143.64   9.722%   $157.6047   $157.60   $157.60   $157.60  
  Purchase #7 $67.46   9.195%   $73.6629   $73.66   $73.65   $73.70  
  7 purchase totals = $1,051.26       $1,148.5030   $1,148.49   $1,148.55   $1,148.40