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	$186.53	7.711%	$200.9133	$200.91	$200.90	$200.90
Purchase #2	$157.48	9.105%	$171.8186	$171.82	$171.80	$171.80
Purchase #3	$212.39	4.583%	$222.1238	$222.12	$222.10	$222.10
Purchase #4	$9.36	5.231%	$9.8496	$9.85	$9.85	$9.80
Purchase #5	$221.86	4.740%	$232.3762	$232.38	$232.40	$232.40
Purchase #6	$104.54	13.845%	$119.0136	$119.01	$119.00	$119.00
Purchase #7	$53.53	6.226%	$56.8628	$56.86	$56.85	$56.90
7 purchase totals =	$945.69		$1,012.9579	$1,012.95	$1,012.90	$1,012.90