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	$68.33	6.719%	$72.9211	$72.92	$72.90	$72.90
Purchase #2	$202.79	11.137%	$225.3747	$225.37	$225.35	$225.40
Purchase #3	$196.72	13.103%	$222.4962	$222.50	$222.50	$222.50
Purchase #4	$202.48	8.709%	$220.114	$220.11	$220.10	$220.10
Purchase #5	$237.58	11.212%	$264.2175	$264.22	$264.20	$264.20
Purchase #6	$39.54	7.412%	$42.4707	$42.47	$42.45	$42.50
Purchase #7	$242.61	11.701%	$270.9978	$271.00	$271.00	$271.00
7 purchase totals =	$1,190.05		$1,318.5920	$1,318.59	$1,318.50	$1,318.60