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 $22.85   13.675%   $25.9747   $25.97   $25.95   $26.00  
  Purchase #2 $153.83   5.449%   $162.2122   $162.21   $162.20   $162.20  
  Purchase #3 $246.36   12.674%   $277.5837   $277.58   $277.60   $277.60  
  Purchase #4 $197.56   9.471%   $216.2709   $216.27   $216.25   $216.30  
  Purchase #5 $205.62   3.227%   $212.2554   $212.26   $212.25   $212.30  
  Purchase #6 $177.37   9.132%   $193.5674   $193.57   $193.55   $193.60  
  Purchase #7 $202.64   6.613%   $216.0406   $216.04   $216.05   $216.00  
  7 purchase totals = $1,206.23       $1,303.9049   $1,303.90   $1,303.85   $1,304.00