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	$113.76	5.629%	$120.1636	$120.16	$120.15	$120.20
Purchase #2	$96.45	12.543%	$108.5477	$108.55	$108.55	$108.50
Purchase #3	$129.85	7.850%	$140.0432	$140.04	$140.05	$140.00
Purchase #4	$64.57	11.368%	$71.9103	$71.91	$71.90	$71.90
Purchase #5	$221.63	12.783%	$249.961	$249.96	$249.95	$250.00
Purchase #6	$205.68	8.174%	$222.4923	$222.49	$222.50	$222.50
Purchase #7	$196.40	7.207%	$210.5545	$210.55	$210.55	$210.60
7 purchase totals =	$1,028.34		$1,123.6726	$1,123.66	$1,123.65	$1,123.70