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 $240.63   13.725%   $273.6565   $273.66   $273.65   $273.70  
  Purchase #2 $61.52   12.214%   $69.0341   $69.03   $69.05   $69.00  
  Purchase #3 $24.27   4.284%   $25.3097   $25.31   $25.30   $25.30  
  Purchase #4 $216.34   7.320%   $232.1761   $232.18   $232.20   $232.20  
  Purchase #5 $111.62   3.208%   $115.2008   $115.20   $115.20   $115.20  
  Purchase #6 $44.64   7.406%   $47.946   $47.95   $47.95   $47.90  
  Purchase #7 $80.35   5.486%   $84.758   $84.76   $84.75   $84.80  
  7 purchase totals = $779.37       $848.0812   $848.09   $848.10   $848.10