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 $208.76   7.406%   $224.2208   $224.22   $224.20   $224.20  
  Purchase #2 $108.95   12.816%   $122.913   $122.91   $122.90   $122.90  
  Purchase #3 $23.60   5.336%   $24.8593   $24.86   $24.85   $24.90  
  Purchase #4 $169.43   4.588%   $177.2034   $177.20   $177.20   $177.20  
  Purchase #5 $129.65   5.526%   $136.8145   $136.81   $136.80   $136.80  
  Purchase #6 $178.91   3.241%   $184.7085   $184.71   $184.70   $184.70  
  Purchase #7 $126.79   3.370%   $131.0628   $131.06   $131.05   $131.10  
  7 purchase totals = $946.09       $1,001.7823   $1,001.77   $1,001.70   $1,001.80