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 $235.50   4.802%   $246.8087   $246.81   $246.80   $246.80  
  Purchase #2 $230.62   4.611%   $241.2539   $241.25   $241.25   $241.30  
  Purchase #3 $224.38   12.271%   $251.9137   $251.91   $251.90   $251.90  
  Purchase #4 $179.98   12.215%   $201.9646   $201.96   $201.95   $202.00  
  Purchase #5 $146.63   7.536%   $157.68   $157.68   $157.70   $157.70  
  Purchase #6 $169.89   4.691%   $177.8595   $177.86   $177.85   $177.90  
  Purchase #7 $153.44   4.861%   $160.8987   $160.90   $160.90   $160.90  
  7 purchase totals = $1,340.44       $1,438.3791   $1,438.37   $1,438.35   $1,438.50