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 $153.29   13.246%   $173.5948   $173.59   $173.60   $173.60  
  Purchase #2 $241.65   10.267%   $266.4602   $266.46   $266.45   $266.50  
  Purchase #3 $36.64   9.798%   $40.23   $40.23   $40.25   $40.20  
  Purchase #4 $28.43   9.118%   $31.0222   $31.02   $31.00   $31.00  
  Purchase #5 $119.85   8.138%   $129.6034   $129.60   $129.60   $129.60  
  Purchase #6 $173.59   4.677%   $181.7088   $181.71   $181.70   $181.70  
  Purchase #7 $162.36   6.538%   $172.9751   $172.98   $173.00   $173.00  
  7 purchase totals = $915.81       $995.5945   $995.59   $995.60   $995.60