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 $59.92   7.277%   $64.2804   $64.28   $64.30   $64.30  
  Purchase #2 $119.48   10.407%   $131.9143   $131.91   $131.90   $131.90  
  Purchase #3 $5.33   9.812%   $5.853   $5.85   $5.85   $5.90  
  Purchase #4 $95.85   12.378%   $107.7143   $107.71   $107.70   $107.70  
  Purchase #5 $212.46   9.761%   $233.1982   $233.20   $233.20   $233.20  
  Purchase #6 $203.93   13.159%   $230.7651   $230.77   $230.75   $230.80  
  Purchase #7 $15.86   6.253%   $16.8517   $16.85   $16.85   $16.90  
  7 purchase totals = $712.83       $790.5770   $790.57   $790.55   $790.70