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 $178.72   8.727%   $194.3169   $194.32   $194.30   $194.30  
  Purchase #2 $248.31   7.633%   $267.2635   $267.26   $267.25   $267.30  
  Purchase #3 $238.94   4.293%   $249.1977   $249.20   $249.20   $249.20  
  Purchase #4 $58.38   8.273%   $63.2098   $63.21   $63.20   $63.20  
  Purchase #5 $188.93   12.132%   $211.851   $211.85   $211.85   $211.90  
  Purchase #6 $56.47   10.668%   $62.4942   $62.49   $62.50   $62.50  
  Purchase #7 $103.89   5.129%   $109.2185   $109.22   $109.20   $109.20  
  7 purchase totals = $1,073.64       $1,157.5516   $1,157.55   $1,157.50   $1,157.60