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	$50.41	6.646%	$53.7602	$53.76	$53.75	$53.80
Purchase #2	$69.82	11.270%	$77.6887	$77.69	$77.70	$77.70
Purchase #3	$26.57	8.647%	$28.8675	$28.87	$28.85	$28.90
Purchase #4	$135.70	3.807%	$140.8661	$140.87	$140.85	$140.90
Purchase #5	$100.73	8.433%	$109.2246	$109.22	$109.20	$109.20
Purchase #6	$76.42	7.411%	$82.0835	$82.08	$82.10	$82.10
Purchase #7	$65.64	10.464%	$72.5086	$72.51	$72.50	$72.50
7 purchase totals =	$525.29		$564.9992	$565.00	$564.95	$565.10