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 $68.87   10.270%   $75.9429   $75.94   $75.95   $75.90  
  Purchase #2 $104.48   6.860%   $111.6473   $111.65   $111.65   $111.60  
  Purchase #3 $197.69   12.408%   $222.2194   $222.22   $222.20   $222.20  
  Purchase #4 $30.42   6.411%   $32.3702   $32.37   $32.35   $32.40  
  Purchase #5 $205.57   11.213%   $228.6206   $228.62   $228.60   $228.60  
  Purchase #6 $23.91   3.724%   $24.8004   $24.80   $24.80   $24.80  
  Purchase #7 $82.83   13.240%   $93.7967   $93.80   $93.80   $93.80  
  7 purchase totals = $713.77       $789.3975   $789.40   $789.35   $789.30