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 $67.55   8.338%   $73.1823   $73.18   $73.20   $73.20  
  Purchase #2 $194.89   4.614%   $203.8822   $203.88   $203.90   $203.90  
  Purchase #3 $88.25   10.775%   $97.7589   $97.76   $97.75   $97.80  
  Purchase #4 $234.90   13.436%   $266.4612   $266.46   $266.45   $266.50  
  Purchase #5 $233.79   11.231%   $260.047   $260.05   $260.05   $260.00  
  Purchase #6 $177.34   5.443%   $186.9926   $186.99   $187.00   $187.00  
  Purchase #7 $79.68   4.841%   $83.5373   $83.54   $83.55   $83.50  
  7 purchase totals = $1,076.40       $1,171.8615   $1,171.86   $1,171.90   $1,171.90