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	$115.71	13.718%	$131.5831	$131.58	$131.60	$131.60
Purchase #2	$17.25	8.755%	$18.7602	$18.76	$18.75	$18.80
Purchase #3	$40.65	4.328%	$42.4093	$42.41	$42.40	$42.40
Purchase #4	$198.32	4.789%	$207.8175	$207.82	$207.80	$207.80
Purchase #5	$118.37	10.334%	$130.6024	$130.60	$130.60	$130.60
Purchase #6	$78.72	10.364%	$86.8785	$86.88	$86.90	$86.90
Purchase #7	$76.84	7.217%	$82.3855	$82.39	$82.40	$82.40
7 purchase totals =	$645.86		$700.4365	$700.44	$700.45	$700.50