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 $173.42   12.825%   $195.6611   $195.66   $195.65   $195.70  
  Purchase #2 $179.95   13.401%   $204.0651   $204.07   $204.05   $204.10  
  Purchase #3 $114.89   11.615%   $128.2345   $128.23   $128.25   $128.20  
  Purchase #4 $240.47   7.749%   $259.104   $259.10   $259.10   $259.10  
  Purchase #5 $125.99   5.275%   $132.636   $132.64   $132.65   $132.60  
  Purchase #6 $138.70   11.272%   $154.3343   $154.33   $154.35   $154.30  
  Purchase #7 $232.72   5.586%   $245.7197   $245.72   $245.70   $245.70  
  7 purchase totals = $1,206.14       $1,319.7547   $1,319.75   $1,319.75   $1,319.70