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	$111.47	11.610%	$124.4117	$124.41	$124.40	$124.40
Purchase #2	$45.57	6.557%	$48.558	$48.56	$48.55	$48.60
Purchase #3	$167.35	11.781%	$187.0655	$187.07	$187.05	$187.10
Purchase #4	$93.58	3.517%	$96.8712	$96.87	$96.85	$96.90
Purchase #5	$67.44	5.295%	$71.0109	$71.01	$71.00	$71.00
Purchase #6	$30.25	3.837%	$31.4107	$31.41	$31.40	$31.40
Purchase #7	$63.66	12.222%	$71.4405	$71.44	$71.45	$71.40
7 purchase totals =	$579.32		$630.7685	$630.77	$630.70	$630.80