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 $98.46   13.683%   $111.9323   $111.93   $111.95   $111.90  
  Purchase #2 $209.26   12.774%   $235.9909   $235.99   $236.00   $236.00  
  Purchase #3 $53.44   13.682%   $60.7517   $60.75   $60.75   $60.80  
  Purchase #4 $70.26   5.342%   $74.0133   $74.01   $74.00   $74.00  
  Purchase #5 $227.72   4.106%   $237.0702   $237.07   $237.05   $237.10  
  Purchase #6 $200.54   13.330%   $227.272   $227.27   $227.25   $227.30  
  Purchase #7 $75.82   10.160%   $83.5233   $83.52   $83.50   $83.50  
  7 purchase totals = $935.50       $1,030.5537   $1,030.54   $1,030.50   $1,030.60