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 $233.92   7.405%   $251.2418   $251.24   $251.25   $251.20  
  Purchase #2 $38.77   9.352%   $42.3958   $42.40   $42.40   $42.40  
  Purchase #3 $168.62   9.276%   $184.2612   $184.26   $184.25   $184.30  
  Purchase #4 $60.73   8.550%   $65.9224   $65.92   $65.90   $65.90  
  Purchase #5 $171.39   9.505%   $187.6806   $187.68   $187.70   $187.70  
  Purchase #6 $110.67   7.715%   $119.2082   $119.21   $119.20   $119.20  
  Purchase #7 $93.42   9.427%   $102.2267   $102.23   $102.25   $102.20  
  7 purchase totals = $877.52       $952.9367   $952.94   $952.95   $952.90