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 $56.89   5.399%   $59.9615   $59.96   $59.95   $60.00  
  Purchase #2 $157.49   9.159%   $171.9145   $171.91   $171.90   $171.90  
  Purchase #3 $122.58   11.735%   $136.9648   $136.96   $136.95   $137.00  
  Purchase #4 $75.29   4.583%   $78.7405   $78.74   $78.75   $78.70  
  Purchase #5 $232.66   7.124%   $249.2347   $249.23   $249.25   $249.20  
  Purchase #6 $122.40   10.856%   $135.6877   $135.69   $135.70   $135.70  
  Purchase #7 $202.91   10.169%   $223.5439   $223.54   $223.55   $223.50  
  7 purchase totals = $970.22       $1,056.0476   $1,056.03   $1,056.05   $1,056.00