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 $24.77   5.621%   $26.1623   $26.16   $26.15   $26.20  
  Purchase #2 $230.79   6.553%   $245.9137   $245.91   $245.90   $245.90  
  Purchase #3 $22.58   13.857%   $25.7089   $25.71   $25.70   $25.70  
  Purchase #4 $220.89   5.399%   $232.8159   $232.82   $232.80   $232.80  
  Purchase #5 $168.27   12.524%   $189.3441   $189.34   $189.35   $189.30  
  Purchase #6 $127.61   4.312%   $133.1125   $133.11   $133.10   $133.10  
  Purchase #7 $111.39   13.421%   $126.3397   $126.34   $126.35   $126.30  
  7 purchase totals = $906.30       $979.3971   $979.39   $979.35   $979.30