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 $200.42   6.124%   $212.6937   $212.69   $212.70   $212.70  
  Purchase #2 $220.71   8.219%   $238.8502   $238.85   $238.85   $238.90  
  Purchase #3 $40.61   6.596%   $43.2886   $43.29   $43.30   $43.30  
  Purchase #4 $92.61   6.539%   $98.6658   $98.67   $98.65   $98.70  
  Purchase #5 $15.68   3.350%   $16.2053   $16.21   $16.20   $16.20  
  Purchase #6 $49.29   4.242%   $51.3809   $51.38   $51.40   $51.40  
  Purchase #7 $84.86   12.650%   $95.5948   $95.59   $95.60   $95.60  
  7 purchase totals = $704.18       $756.6793   $756.68   $756.70   $756.80