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 $70.43   10.679%   $77.9512   $77.95   $77.95   $78.00  
  Purchase #2 $206.97   13.724%   $235.3746   $235.37   $235.35   $235.40  
  Purchase #3 $101.95   12.570%   $114.7651   $114.77   $114.75   $114.80  
  Purchase #4 $25.44   8.678%   $27.6477   $27.65   $27.65   $27.60  
  Purchase #5 $29.79   7.621%   $32.0603   $32.06   $32.05   $32.10  
  Purchase #6 $116.50   5.547%   $122.9623   $122.96   $122.95   $123.00  
  Purchase #7 $242.76   4.248%   $253.0724   $253.07   $253.05   $253.10  
  7 purchase totals = $793.84       $863.8336   $863.83   $863.75   $864.00