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 $53.51   12.578%   $60.2405   $60.24   $60.25   $60.20  
  Purchase #2 $157.53   6.434%   $167.6655   $167.67   $167.65   $167.70  
  Purchase #3 $218.74   6.286%   $232.49   $232.49   $232.50   $232.50  
  Purchase #4 $50.53   7.498%   $54.3187   $54.32   $54.30   $54.30  
  Purchase #5 $142.59   7.193%   $152.8465   $152.85   $152.85   $152.80  
  Purchase #6 $171.31   8.538%   $185.9364   $185.94   $185.95   $185.90  
  Purchase #7 $156.63   12.852%   $176.7601   $176.76   $176.75   $176.80  
  7 purchase totals = $950.84       $1,030.2577   $1,030.27   $1,030.25   $1,030.20