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 $148.74   5.736%   $157.2717   $157.27   $157.25   $157.30  
  Purchase #2 $194.61   8.619%   $211.3834   $211.38   $211.40   $211.40  
  Purchase #3 $196.33   4.668%   $205.4947   $205.49   $205.50   $205.50  
  Purchase #4 $250.68   5.473%   $264.3997   $264.40   $264.40   $264.40  
  Purchase #5 $49.49   10.358%   $54.6162   $54.62   $54.60   $54.60  
  Purchase #6 $194.64   6.709%   $207.6984   $207.70   $207.70   $207.70  
  Purchase #7 $248.64   7.385%   $267.0021   $267.00   $267.00   $267.00  
  7 purchase totals = $1,283.13       $1,367.8662   $1,367.86   $1,367.85   $1,367.90