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	$245.58	5.213%	$258.3821	$258.38	$258.40	$258.40
Purchase #2	$161.55	6.133%	$171.4579	$171.46	$171.45	$171.50
Purchase #3	$130.71	4.719%	$136.8782	$136.88	$136.90	$136.90
Purchase #4	$72.85	12.712%	$82.1107	$82.11	$82.10	$82.10
Purchase #5	$55.73	10.215%	$61.4228	$61.42	$61.40	$61.40
Purchase #6	$64.69	10.127%	$71.2412	$71.24	$71.25	$71.20
Purchase #7	$79.99	10.401%	$88.3098	$88.31	$88.30	$88.30
7 purchase totals =	$811.10		$869.8027	$869.80	$869.80	$869.80