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 $212.98   13.201%   $241.0955   $241.10   $241.10   $241.10  
  Purchase #2 $26.79   3.151%   $27.6342   $27.63   $27.65   $27.60  
  Purchase #3 $67.61   3.132%   $69.7275   $69.73   $69.75   $69.70  
  Purchase #4 $245.90   5.243%   $258.7925   $258.79   $258.80   $258.80  
  Purchase #5 $195.85   5.541%   $206.702   $206.70   $206.70   $206.70  
  Purchase #6 $213.60   9.457%   $233.8002   $233.80   $233.80   $233.80  
  Purchase #7 $173.84   13.585%   $197.4562   $197.46   $197.45   $197.50  
  7 purchase totals = $1,136.57       $1,235.2081   $1,235.21   $1,235.25   $1,235.20