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	$120.90	3.227%	$124.8014	$124.80	$124.80	$124.80
Purchase #2	$90.74	11.416%	$101.0989	$101.10	$101.10	$101.10
Purchase #3	$160.87	11.349%	$179.1271	$179.13	$179.15	$179.10
Purchase #4	$104.59	4.299%	$109.0863	$109.09	$109.10	$109.10
Purchase #5	$40.37	6.840%	$43.1313	$43.13	$43.15	$43.10
Purchase #6	$19.54	10.353%	$21.563	$21.56	$21.55	$21.60
Purchase #7	$98.41	12.180%	$110.3963	$110.40	$110.40	$110.40
7 purchase totals =	$635.42		$689.2043	$689.21	$689.25	$689.20