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 $212.47   13.832%   $241.8589   $241.86   $241.85   $241.90  
  Purchase #2 $140.28   13.783%   $159.6148   $159.61   $159.60   $159.60  
  Purchase #3 $214.87   4.504%   $224.5477   $224.55   $224.55   $224.50  
  Purchase #4 $60.80   8.346%   $65.8744   $65.87   $65.85   $65.90  
  Purchase #5 $98.37   11.240%   $109.4268   $109.43   $109.45   $109.40  
  Purchase #6 $226.31   11.711%   $252.8132   $252.81   $252.80   $252.80  
  Purchase #7 $211.64   13.772%   $240.7871   $240.79   $240.80   $240.80  
  7 purchase totals = $1,164.74       $1,294.9229   $1,294.92   $1,294.90   $1,294.90