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 $86.89   8.466%   $94.2461   $94.25   $94.25   $94.20  
  Purchase #2 $17.53   6.401%   $18.6521   $18.65   $18.65   $18.70  
  Purchase #3 $81.35   7.576%   $87.5131   $87.51   $87.50   $87.50  
  Purchase #4 $208.99   8.320%   $226.378   $226.38   $226.40   $226.40  
  Purchase #5 $237.34   4.235%   $247.3913   $247.39   $247.40   $247.40  
  Purchase #6 $81.65   9.454%   $89.3692   $89.37   $89.35   $89.40  
  Purchase #7 $30.37   4.304%   $31.6771   $31.68   $31.70   $31.70  
  7 purchase totals = $744.12       $795.2269   $795.23   $795.25   $795.30