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 $183.88   13.353%   $208.4335   $208.43   $208.45   $208.40  
  Purchase #2 $34.41   12.257%   $38.6276   $38.63   $38.65   $38.60  
  Purchase #3 $140.52   12.649%   $158.2944   $158.29   $158.30   $158.30  
  Purchase #4 $235.61   4.612%   $246.4763   $246.48   $246.50   $246.50  
  Purchase #5 $161.86   11.536%   $180.5322   $180.53   $180.55   $180.50  
  Purchase #6 $59.82   6.585%   $63.7591   $63.76   $63.75   $63.80  
  Purchase #7 $16.63   4.362%   $17.3554   $17.36   $17.35   $17.40  
  7 purchase totals = $832.73       $913.4785   $913.48   $913.55   $913.50