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 $165.25   11.682%   $184.5545   $184.55   $184.55   $184.60  
  Purchase #2 $165.66   10.666%   $183.3293   $183.33   $183.35   $183.30  
  Purchase #3 $105.32   12.508%   $118.4934   $118.49   $118.50   $118.50  
  Purchase #4 $142.86   10.206%   $157.4403   $157.44   $157.45   $157.40  
  Purchase #5 $116.46   5.852%   $123.2752   $123.28   $123.30   $123.30  
  Purchase #6 $213.68   3.818%   $221.8383   $221.84   $221.85   $221.80  
  Purchase #7 $33.55   6.563%   $35.7519   $35.75   $35.75   $35.80  
  7 purchase totals = $942.78       $1,024.6829   $1,024.68   $1,024.75   $1,024.70