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 $56.84   3.724%   $58.9567   $58.96   $58.95   $59.00  
  Purchase #2 $170.96   5.126%   $179.7234   $179.72   $179.70   $179.70  
  Purchase #3 $48.44   12.433%   $54.4625   $54.46   $54.45   $54.50  
  Purchase #4 $207.63   11.401%   $231.3019   $231.30   $231.30   $231.30  
  Purchase #5 $19.95   4.215%   $20.7909   $20.79   $20.80   $20.80  
  Purchase #6 $29.68   5.817%   $31.4065   $31.41   $31.40   $31.40  
  Purchase #7 $131.97   13.757%   $150.1251   $150.13   $150.15   $150.10  
  7 purchase totals = $665.47       $726.7670   $726.77   $726.75   $726.80