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 $184.76   5.396%   $194.7296   $194.73   $194.75   $194.70  
  Purchase #2 $242.70   12.591%   $273.2584   $273.26   $273.25   $273.30  
  Purchase #3 $7.90   4.772%   $8.277   $8.28   $8.30   $8.30  
  Purchase #4 $162.93   5.346%   $171.6402   $171.64   $171.65   $171.60  
  Purchase #5 $153.90   8.769%   $167.3955   $167.40   $167.40   $167.40  
  Purchase #6 $193.98   5.271%   $204.2047   $204.20   $204.20   $204.20  
  Purchase #7 $221.61   4.151%   $230.809   $230.81   $230.80   $230.80  
  7 purchase totals = $1,167.78       $1,250.3144   $1,250.32   $1,250.35   $1,250.30