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 $222.43   4.860%   $233.2401   $233.24   $233.25   $233.20  
  Purchase #2 $165.88   13.757%   $188.7001   $188.70   $188.70   $188.70  
  Purchase #3 $50.37   5.822%   $53.3025   $53.30   $53.30   $53.30  
  Purchase #4 $167.65   9.490%   $183.56   $183.56   $183.55   $183.60  
  Purchase #5 $160.42   8.435%   $173.9514   $173.95   $173.95   $174.00  
  Purchase #6 $198.72   13.784%   $226.1116   $226.11   $226.10   $226.10  
  Purchase #7 $191.46   3.789%   $198.7144   $198.71   $198.70   $198.70  
  7 purchase totals = $1,156.93       $1,257.5801   $1,257.57   $1,257.55   $1,257.60