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	$202.78	3.837%	$210.5607	$210.56	$210.55	$210.60
Purchase #2	$163.92	9.862%	$180.0858	$180.09	$180.10	$180.10
Purchase #3	$127.57	8.104%	$137.9083	$137.91	$137.90	$137.90
Purchase #4	$80.80	3.390%	$83.5391	$83.54	$83.55	$83.50
Purchase #5	$47.25	11.676%	$52.7669	$52.77	$52.75	$52.80
Purchase #6	$227.67	11.747%	$254.4144	$254.41	$254.40	$254.40
Purchase #7	$77.50	6.824%	$82.7886	$82.79	$82.80	$82.80
7 purchase totals =	$927.49		$1,002.0638	$1,002.07	$1,002.05	$1,002.10