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	$71.54	11.534%	$79.7914	$79.79	$79.80	$79.80
Purchase #2	$175.33	4.469%	$183.1655	$183.17	$183.15	$183.20
Purchase #3	$61.96	4.182%	$64.5512	$64.55	$64.55	$64.60
Purchase #4	$98.80	10.645%	$109.3173	$109.32	$109.30	$109.30
Purchase #5	$154.91	11.462%	$172.6658	$172.67	$172.65	$172.70
Purchase #6	$223.33	8.411%	$242.1143	$242.11	$242.10	$242.10
Purchase #7	$64.86	11.265%	$72.1665	$72.17	$72.15	$72.20
7 purchase totals =	$850.73		$923.7720	$923.78	$923.70	$923.90