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 $61.61   8.193%   $66.6577   $66.66   $66.65   $66.70  
  Purchase #2 $167.98   11.802%   $187.805   $187.81   $187.80   $187.80  
  Purchase #3 $37.92   7.852%   $40.8975   $40.90   $40.90   $40.90  
  Purchase #4 $161.69   10.241%   $178.2487   $178.25   $178.25   $178.20  
  Purchase #5 $72.35   13.145%   $81.8604   $81.86   $81.85   $81.90  
  Purchase #6 $202.45   13.112%   $228.9952   $229.00   $229.00   $229.00  
  Purchase #7 $45.75   4.529%   $47.822   $47.82   $47.80   $47.80  
  7 purchase totals = $749.75       $832.2865   $832.30   $832.25   $832.30