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	$150.36	13.150%	$170.1323	$170.13	$170.15	$170.10
Purchase #2	$71.35	6.571%	$76.0384	$76.04	$76.05	$76.00
Purchase #3	$159.77	7.186%	$171.2511	$171.25	$171.25	$171.30
Purchase #4	$74.91	10.761%	$82.9711	$82.97	$82.95	$83.00
Purchase #5	$240.34	3.647%	$249.1052	$249.11	$249.10	$249.10
Purchase #6	$55.68	6.830%	$59.4829	$59.48	$59.50	$59.50
Purchase #7	$83.71	6.543%	$89.1871	$89.19	$89.20	$89.20
7 purchase totals =	$836.12		$898.1681	$898.17	$898.20	$898.20