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 $66.37   10.726%   $73.4888   $73.49   $73.50   $73.50  
  Purchase #2 $24.58   9.671%   $26.9571   $26.96   $26.95   $27.00  
  Purchase #3 $120.57   3.116%   $124.327   $124.33   $124.35   $124.30  
  Purchase #4 $133.67   3.419%   $138.2402   $138.24   $138.25   $138.20  
  Purchase #5 $203.90   7.749%   $219.7002   $219.70   $219.70   $219.70  
  Purchase #6 $67.71   12.394%   $76.102   $76.10   $76.10   $76.10  
  Purchase #7 $39.83   3.840%   $41.3595   $41.36   $41.35   $41.40  
  7 purchase totals = $656.63       $700.1748   $700.18   $700.20   $700.20