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 $247.48   5.578%   $261.2844   $261.28   $261.30   $261.30  
  Purchase #2 $165.87   9.535%   $181.6857   $181.69   $181.70   $181.70  
  Purchase #3 $32.82   6.644%   $35.0006   $35.00   $35.00   $35.00  
  Purchase #4 $227.55   5.457%   $239.9674   $239.97   $239.95   $240.00  
  Purchase #5 $16.97   13.818%   $19.3149   $19.31   $19.30   $19.30  
  Purchase #6 $238.46   7.116%   $255.4288   $255.43   $255.45   $255.40  
  Purchase #7 $248.84   13.379%   $282.1323   $282.13   $282.15   $282.10  
  7 purchase totals = $1,177.99       $1,274.8141   $1,274.81   $1,274.85   $1,274.80