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 $65.86   8.186%   $71.2513   $71.25   $71.25   $71.30  
  Purchase #2 $166.97   8.775%   $181.6216   $181.62   $181.60   $181.60  
  Purchase #3 $52.32   7.355%   $56.1681   $56.17   $56.15   $56.20  
  Purchase #4 $192.58   9.602%   $211.0715   $211.07   $211.05   $211.10  
  Purchase #5 $26.81   10.657%   $29.6671   $29.67   $29.65   $29.70  
  Purchase #6 $150.75   9.502%   $165.0743   $165.07   $165.05   $165.10  
  Purchase #7 $38.63   3.644%   $40.0377   $40.04   $40.05   $40.00  
  7 purchase totals = $693.92       $754.8916   $754.89   $754.80   $755.00