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 $148.67   13.162%   $168.2379   $168.24   $168.25   $168.20  
  Purchase #2 $52.96   6.737%   $56.5279   $56.53   $56.55   $56.50  
  Purchase #3 $161.85   6.187%   $171.8637   $171.86   $171.85   $171.90  
  Purchase #4 $154.67   7.774%   $166.694   $166.69   $166.70   $166.70  
  Purchase #5 $155.71   11.255%   $173.2352   $173.24   $173.25   $173.20  
  Purchase #6 $224.92   5.759%   $237.8731   $237.87   $237.85   $237.90  
  Purchase #7 $160.46   11.465%   $178.8567   $178.86   $178.85   $178.90  
  7 purchase totals = $1,059.24       $1,153.2885   $1,153.29   $1,153.30   $1,153.30