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 $116.77   9.479%   $127.8386   $127.84   $127.85   $127.80  
  Purchase #2 $197.96   8.573%   $214.9311   $214.93   $214.95   $214.90  
  Purchase #3 $182.66   7.572%   $196.491   $196.49   $196.50   $196.50  
  Purchase #4 $173.27   4.837%   $181.6511   $181.65   $181.65   $181.70  
  Purchase #5 $22.32   12.780%   $25.1725   $25.17   $25.15   $25.20  
  Purchase #6 $236.26   13.278%   $267.6306   $267.63   $267.65   $267.60  
  Purchase #7 $44.88   3.824%   $46.5962   $46.60   $46.60   $46.60  
  7 purchase totals = $974.12       $1,060.3111   $1,060.31   $1,060.35   $1,060.30