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 $188.90   9.856%   $207.518   $207.52   $207.50   $207.50  
  Purchase #2 $101.83   13.490%   $115.5669   $115.57   $115.55   $115.60  
  Purchase #3 $104.79   11.210%   $116.537   $116.54   $116.55   $116.50  
  Purchase #4 $43.51   11.222%   $48.3927   $48.39   $48.40   $48.40  
  Purchase #5 $164.86   11.525%   $183.8601   $183.86   $183.85   $183.90  
  Purchase #6 $182.71   5.506%   $192.77   $192.77   $192.75   $192.80  
  Purchase #7 $10.96   8.225%   $11.8615   $11.86   $11.85   $11.90  
  7 purchase totals = $797.56       $876.5062   $876.51   $876.45   $876.60