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 $114.57   8.766%   $124.6132   $124.61   $124.60   $124.60  
  Purchase #2 $217.90   9.572%   $238.7574   $238.76   $238.75   $238.80  
  Purchase #3 $167.92   8.310%   $181.8742   $181.87   $181.85   $181.90  
  Purchase #4 $196.59   6.300%   $208.9752   $208.98   $209.00   $209.00  
  Purchase #5 $151.88   10.685%   $168.1084   $168.11   $168.10   $168.10  
  Purchase #6 $117.64   13.402%   $133.4061   $133.41   $133.40   $133.40  
  Purchase #7 $142.25   6.565%   $151.5887   $151.59   $151.60   $151.60  
  7 purchase totals = $1,108.75       $1,207.3232   $1,207.33   $1,207.30   $1,207.40