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 $150.77   11.354%   $167.8884   $167.89   $167.90   $167.90  
  Purchase #2 $209.32   13.289%   $237.1365   $237.14   $237.15   $237.10  
  Purchase #3 $57.89   11.558%   $64.5809   $64.58   $64.60   $64.60  
  Purchase #4 $23.48   9.603%   $25.7348   $25.73   $25.75   $25.70  
  Purchase #5 $119.70   12.694%   $134.8947   $134.89   $134.90   $134.90  
  Purchase #6 $218.60   9.856%   $240.1452   $240.15   $240.15   $240.10  
  Purchase #7 $174.33   13.729%   $198.2638   $198.26   $198.25   $198.30  
  7 purchase totals = $954.09       $1,068.6443   $1,068.64   $1,068.70   $1,068.60