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 $218.90   10.465%   $241.8079   $241.81   $241.80   $241.80  
  Purchase #2 $220.64   6.641%   $235.2927   $235.29   $235.30   $235.30  
  Purchase #3 $54.44   7.611%   $58.5834   $58.58   $58.60   $58.60  
  Purchase #4 $95.27   8.247%   $103.1269   $103.13   $103.15   $103.10  
  Purchase #5 $61.88   5.670%   $65.3886   $65.39   $65.40   $65.40  
  Purchase #6 $141.65   4.103%   $147.4619   $147.46   $147.45   $147.50  
  Purchase #7 $69.36   9.537%   $75.9749   $75.97   $75.95   $76.00  
  7 purchase totals = $862.14       $927.6363   $927.63   $927.65   $927.70