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 $113.32   11.612%   $126.4787   $126.48   $126.50   $126.50  
  Purchase #2 $177.81   8.292%   $192.554   $192.55   $192.55   $192.60  
  Purchase #3 $10.40   8.775%   $11.3126   $11.31   $11.30   $11.30  
  Purchase #4 $132.67   6.605%   $141.4329   $141.43   $141.45   $141.40  
  Purchase #5 $36.95   7.283%   $39.6411   $39.64   $39.65   $39.60  
  Purchase #6 $192.52   6.104%   $204.2714   $204.27   $204.25   $204.30  
  Purchase #7 $28.70   7.648%   $30.895   $30.90   $30.90   $30.90  
  7 purchase totals = $692.37       $746.5857   $746.58   $746.60   $746.60