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 $71.87   6.761%   $76.7291   $76.73   $76.75   $76.70  
  Purchase #2 $131.26   8.827%   $142.8463   $142.85   $142.85   $142.80  
  Purchase #3 $241.77   4.118%   $251.7261   $251.73   $251.75   $251.70  
  Purchase #4 $29.35   13.522%   $33.3187   $33.32   $33.30   $33.30  
  Purchase #5 $65.71   8.256%   $71.135   $71.14   $71.15   $71.10  
  Purchase #6 $204.35   5.218%   $215.013   $215.01   $215.00   $215.00  
  Purchase #7 $40.77   13.736%   $46.3702   $46.37   $46.35   $46.40  
  7 purchase totals = $785.08       $837.1384   $837.15   $837.15   $837.00