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 $107.98   8.470%   $117.1259   $117.13   $117.15   $117.10  
  Purchase #2 $248.62   8.429%   $269.5762   $269.58   $269.60   $269.60  
  Purchase #3 $242.47   10.711%   $268.441   $268.44   $268.45   $268.40  
  Purchase #4 $60.86   6.208%   $64.6382   $64.64   $64.65   $64.60  
  Purchase #5 $121.26   11.295%   $134.9563   $134.96   $134.95   $135.00  
  Purchase #6 $136.60   4.104%   $142.2061   $142.21   $142.20   $142.20  
  Purchase #7 $60.48   10.707%   $66.9556   $66.96   $66.95   $67.00  
  7 purchase totals = $978.27       $1,063.8993   $1,063.92   $1,063.95   $1,063.90