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 $58.91   3.106%   $60.7397   $60.74   $60.75   $60.70  
  Purchase #2 $86.61   6.426%   $92.1756   $92.18   $92.20   $92.20  
  Purchase #3 $216.63   10.550%   $239.4845   $239.48   $239.50   $239.50  
  Purchase #4 $79.54   8.225%   $86.0822   $86.08   $86.10   $86.10  
  Purchase #5 $182.72   11.314%   $203.3929   $203.39   $203.40   $203.40  
  Purchase #6 $26.95   3.428%   $27.8738   $27.87   $27.85   $27.90  
  Purchase #7 $75.74   9.619%   $83.0254   $83.03   $83.05   $83.00  
  7 purchase totals = $727.10       $792.7741   $792.77   $792.85   $792.80