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 $153.70   13.351%   $174.2205   $174.22   $174.20   $174.20  
  Purchase #2 $242.96   7.787%   $261.8793   $261.88   $261.90   $261.90  
  Purchase #3 $171.41   9.504%   $187.7008   $187.70   $187.70   $187.70  
  Purchase #4 $89.36   5.862%   $94.5983   $94.60   $94.60   $94.60  
  Purchase #5 $237.35   4.414%   $247.8266   $247.83   $247.85   $247.80  
  Purchase #6 $226.48   6.407%   $240.9906   $240.99   $241.00   $241.00  
  Purchase #7 $83.44   5.851%   $88.3221   $88.32   $88.30   $88.30  
  7 purchase totals = $1,204.70       $1,295.5382   $1,295.54   $1,295.55   $1,295.50