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 $138.49   9.683%   $151.9   $151.90   $151.90   $151.90  
  Purchase #2 $216.82   8.783%   $235.8633   $235.86   $235.85   $235.90  
  Purchase #3 $8.92   12.366%   $10.023   $10.02   $10.00   $10.00  
  Purchase #4 $114.62   8.496%   $124.3581   $124.36   $124.35   $124.40  
  Purchase #5 $245.95   9.487%   $269.2833   $269.28   $269.30   $269.30  
  Purchase #6 $184.72   13.252%   $209.1991   $209.20   $209.20   $209.20  
  Purchase #7 $96.40   5.565%   $101.7647   $101.76   $101.75   $101.80  
  7 purchase totals = $1,005.92       $1,102.3915   $1,102.38   $1,102.35   $1,102.50