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 $106.60   9.553%   $116.7835   $116.78   $116.80   $116.80  
  Purchase #2 $53.77   8.748%   $58.4738   $58.47   $58.45   $58.50  
  Purchase #3 $159.89   13.374%   $181.2737   $181.27   $181.25   $181.30  
  Purchase #4 $171.98   4.602%   $179.8945   $179.89   $179.90   $179.90  
  Purchase #5 $56.52   7.231%   $60.607   $60.61   $60.60   $60.60  
  Purchase #6 $248.84   8.725%   $270.5513   $270.55   $270.55   $270.60  
  Purchase #7 $197.40   8.744%   $214.6607   $214.66   $214.65   $214.70  
  7 purchase totals = $995.00       $1,082.2445   $1,082.23   $1,082.20   $1,082.40