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	$76.56	10.424%	$84.5406	$84.54	$84.55	$84.50
Purchase #2	$120.98	7.640%	$130.2229	$130.22	$130.20	$130.20
Purchase #3	$133.72	10.351%	$147.5614	$147.56	$147.55	$147.60
Purchase #4	$109.78	12.475%	$123.4751	$123.48	$123.50	$123.50
Purchase #5	$129.29	9.334%	$141.3579	$141.36	$141.35	$141.40
Purchase #6	$205.71	10.503%	$227.3157	$227.32	$227.30	$227.30
Purchase #7	$81.51	5.525%	$86.0134	$86.01	$86.00	$86.00
7 purchase totals =	$857.55		$940.4870	$940.49	$940.45	$940.50