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 $149.70   11.592%   $167.0532   $167.05   $167.05   $167.10  
  Purchase #2 $60.62   6.472%   $64.5433   $64.54   $64.55   $64.50  
  Purchase #3 $41.86   11.594%   $46.7132   $46.71   $46.70   $46.70  
  Purchase #4 $114.85   10.742%   $127.1872   $127.19   $127.20   $127.20  
  Purchase #5 $103.57   10.791%   $114.7462   $114.75   $114.75   $114.70  
  Purchase #6 $230.77   7.573%   $248.2462   $248.25   $248.25   $248.20  
  Purchase #7 $227.36   7.780%   $245.0486   $245.05   $245.05   $245.00  
  7 purchase totals = $928.73       $1,013.5379   $1,013.54   $1,013.55   $1,013.40