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 $163.60   7.496%   $175.8635   $175.86   $175.85   $175.90  
  Purchase #2 $6.34   3.647%   $6.5712   $6.57   $6.55   $6.60  
  Purchase #3 $134.70   4.327%   $140.5285   $140.53   $140.55   $140.50  
  Purchase #4 $120.76   8.181%   $130.6394   $130.64   $130.65   $130.60  
  Purchase #5 $153.72   9.310%   $168.0313   $168.03   $168.05   $168.00  
  Purchase #6 $234.26   4.345%   $244.4386   $244.44   $244.45   $244.40  
  Purchase #7 $236.75   12.775%   $266.9948   $266.99   $267.00   $267.00  
  7 purchase totals = $1,050.13       $1,133.0673   $1,133.06   $1,133.10   $1,133.00