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 $41.44   7.826%   $44.6831   $44.68   $44.70   $44.70  
  Purchase #2 $183.99   11.317%   $204.8121   $204.81   $204.80   $204.80  
  Purchase #3 $147.25   13.398%   $166.9786   $166.98   $167.00   $167.00  
  Purchase #4 $239.41   11.584%   $267.1433   $267.14   $267.15   $267.10  
  Purchase #5 $139.34   5.641%   $147.2002   $147.20   $147.20   $147.20  
  Purchase #6 $44.41   3.619%   $46.0172   $46.02   $46.00   $46.00  
  Purchase #7 $63.45   4.549%   $66.3363   $66.34   $66.35   $66.30  
  7 purchase totals = $859.29       $943.1708   $943.17   $943.20   $943.10