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	$221.45	6.271%	$235.3371	$235.34	$235.35	$235.30
Purchase #2	$192.33	4.367%	$200.7291	$200.73	$200.75	$200.70
Purchase #3	$56.31	5.241%	$59.2612	$59.26	$59.25	$59.30
Purchase #4	$59.45	3.333%	$61.4315	$61.43	$61.45	$61.40
Purchase #5	$81.34	6.708%	$86.7963	$86.80	$86.80	$86.80
Purchase #6	$178.30	10.315%	$196.6916	$196.69	$196.70	$196.70
Purchase #7	$119.89	8.498%	$130.0783	$130.08	$130.10	$130.10
7 purchase totals =	$909.07		$970.3251	$970.33	$970.40	$970.30