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 $184.58   10.141%   $203.2983   $203.30   $203.30   $203.30  
  Purchase #2 $126.83   11.133%   $140.95   $140.95   $140.95   $141.00  
  Purchase #3 $197.56   11.622%   $220.5204   $220.52   $220.50   $220.50  
  Purchase #4 $78.64   11.381%   $87.59   $87.59   $87.60   $87.60  
  Purchase #5 $21.27   10.104%   $23.4191   $23.42   $23.40   $23.40  
  Purchase #6 $165.92   5.654%   $175.3011   $175.30   $175.30   $175.30  
  Purchase #7 $242.52   4.383%   $253.1497   $253.15   $253.15   $253.10  
  7 purchase totals = $1,017.32       $1,104.2286   $1,104.23   $1,104.20   $1,104.20