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 $55.62   3.514%   $57.5745   $57.57   $57.55   $57.60  
  Purchase #2 $216.90   11.744%   $242.3727   $242.37   $242.35   $242.40  
  Purchase #3 $233.44   5.195%   $245.5672   $245.57   $245.55   $245.60  
  Purchase #4 $181.80   8.489%   $197.233   $197.23   $197.25   $197.20  
  Purchase #5 $169.97   9.512%   $186.1375   $186.14   $186.15   $186.10  
  Purchase #6 $130.74   8.424%   $141.7535   $141.75   $141.75   $141.80  
  Purchase #7 $219.36   7.318%   $235.4128   $235.41   $235.40   $235.40  
  7 purchase totals = $1,207.83       $1,306.0512   $1,306.04   $1,306.00   $1,306.10