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 $75.63   11.821%   $84.5702   $84.57   $84.55   $84.60  
  Purchase #2 $206.97   12.505%   $232.8516   $232.85   $232.85   $232.90  
  Purchase #3 $12.43   10.446%   $13.7284   $13.73   $13.75   $13.70  
  Purchase #4 $106.65   13.872%   $121.4445   $121.44   $121.45   $121.40  
  Purchase #5 $46.76   11.245%   $52.0182   $52.02   $52.00   $52.00  
  Purchase #6 $208.33   8.587%   $226.2193   $226.22   $226.20   $226.20  
  Purchase #7 $25.99   6.814%   $27.761   $27.76   $27.75   $27.80  
  7 purchase totals = $682.76       $758.5932   $758.59   $758.55   $758.60