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 $58.95   13.649%   $66.9961   $67.00   $67.00   $67.00  
  Purchase #2 $152.32   7.823%   $164.236   $164.24   $164.25   $164.20  
  Purchase #3 $245.34   7.226%   $263.0683   $263.07   $263.05   $263.10  
  Purchase #4 $71.45   6.417%   $76.0349   $76.03   $76.05   $76.00  
  Purchase #5 $169.45   9.748%   $185.968   $185.97   $185.95   $186.00  
  Purchase #6 $212.86   5.677%   $224.9441   $224.94   $224.95   $224.90  
  Purchase #7 $37.32   3.350%   $38.5702   $38.57   $38.55   $38.60  
  7 purchase totals = $947.69       $1,019.8176   $1,019.82   $1,019.80   $1,019.80