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 $164.88   7.712%   $177.5955   $177.60   $177.60   $177.60  
  Purchase #2 $85.39   9.719%   $93.6891   $93.69   $93.70   $93.70  
  Purchase #3 $103.90   4.122%   $108.1828   $108.18   $108.20   $108.20  
  Purchase #4 $7.32   11.302%   $8.1473   $8.15   $8.15   $8.10  
  Purchase #5 $94.88   7.483%   $101.9799   $101.98   $102.00   $102.00  
  Purchase #6 $58.48   3.524%   $60.5408   $60.54   $60.55   $60.50  
  Purchase #7 $95.98   13.750%   $109.1773   $109.18   $109.20   $109.20  
  7 purchase totals = $610.83       $659.3127   $659.32   $659.40   $659.30