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 $88.64   7.844%   $95.5929   $95.59   $95.60   $95.60  
  Purchase #2 $6.79   13.466%   $7.7043   $7.70   $7.70   $7.70  
  Purchase #3 $160.33   13.469%   $181.9248   $181.92   $181.90   $181.90  
  Purchase #4 $115.33   5.354%   $121.5048   $121.50   $121.50   $121.50  
  Purchase #5 $126.77   12.499%   $142.615   $142.62   $142.60   $142.60  
  Purchase #6 $31.82   9.706%   $34.9084   $34.91   $34.90   $34.90  
  Purchase #7 $239.55   9.157%   $261.4856   $261.49   $261.50   $261.50  
  7 purchase totals = $769.23       $845.7358   $845.73   $845.70   $845.70