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 $69.58   6.151%   $73.8599   $73.86   $73.85   $73.90  
  Purchase #2 $200.67   4.651%   $210.0032   $210.00   $210.00   $210.00  
  Purchase #3 $94.46   9.700%   $103.6226   $103.62   $103.60   $103.60  
  Purchase #4 $131.31   10.582%   $145.2052   $145.21   $145.20   $145.20  
  Purchase #5 $49.58   7.577%   $53.3367   $53.34   $53.35   $53.30  
  Purchase #6 $60.59   9.420%   $66.2976   $66.30   $66.30   $66.30  
  Purchase #7 $99.34   10.642%   $109.9118   $109.91   $109.90   $109.90  
  7 purchase totals = $705.53       $762.2370   $762.24   $762.20   $762.20