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	$114.36	12.111%	$128.2101	$128.21	$128.20	$128.20
Purchase #2	$164.45	6.765%	$175.575	$175.58	$175.60	$175.60
Purchase #3	$88.81	11.336%	$98.8775	$98.88	$98.90	$98.90
Purchase #4	$54.75	9.111%	$59.7383	$59.74	$59.75	$59.70
Purchase #5	$89.49	11.542%	$99.8189	$99.82	$99.80	$99.80
Purchase #6	$194.27	12.632%	$218.8102	$218.81	$218.80	$218.80
Purchase #7	$61.66	12.186%	$69.1739	$69.17	$69.15	$69.20
7 purchase totals =	$767.79		$850.2039	$850.21	$850.20	$850.20