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 $41.41   6.756%   $44.2077   $44.21   $44.20   $44.20  
  Purchase #2 $162.49   4.511%   $169.8199   $169.82   $169.80   $169.80  
  Purchase #3 $161.43   8.236%   $174.7254   $174.73   $174.75   $174.70  
  Purchase #4 $84.97   13.181%   $96.1699   $96.17   $96.15   $96.20  
  Purchase #5 $198.29   8.384%   $214.9146   $214.91   $214.90   $214.90  
  Purchase #6 $135.61   10.400%   $149.7134   $149.71   $149.70   $149.70  
  Purchase #7 $24.48   5.866%   $25.916   $25.92   $25.90   $25.90  
  7 purchase totals = $808.68       $875.4669   $875.47   $875.40   $875.40