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 $65.28   12.736%   $73.5941   $73.59   $73.60   $73.60  
  Purchase #2 $55.90   13.692%   $63.5538   $63.55   $63.55   $63.60  
  Purchase #3 $26.54   8.132%   $28.6982   $28.70   $28.70   $28.70  
  Purchase #4 $50.89   4.430%   $53.1444   $53.14   $53.15   $53.10  
  Purchase #5 $239.47   11.411%   $266.7959   $266.80   $266.80   $266.80  
  Purchase #6 $61.79   6.745%   $65.9577   $65.96   $65.95   $66.00  
  Purchase #7 $12.79   13.454%   $14.5108   $14.51   $14.50   $14.50  
  7 purchase totals = $512.66       $566.2549   $566.25   $566.25   $566.30