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 $142.61   11.258%   $158.665   $158.67   $158.65   $158.70  
  Purchase #2 $181.41   13.665%   $206.1997   $206.20   $206.20   $206.20  
  Purchase #3 $67.49   8.217%   $73.0357   $73.04   $73.05   $73.00  
  Purchase #4 $204.32   13.125%   $231.137   $231.14   $231.15   $231.10  
  Purchase #5 $175.46   12.610%   $197.5855   $197.59   $197.60   $197.60  
  Purchase #6 $187.39   6.754%   $200.0463   $200.05   $200.05   $200.00  
  Purchase #7 $109.32   5.869%   $115.736   $115.74   $115.75   $115.70  
  7 purchase totals = $1,068.00       $1,182.4052   $1,182.43   $1,182.45   $1,182.30