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	$45.43	11.317%	$50.5713	$50.57	$50.55	$50.60
Purchase #2	$89.98	4.758%	$94.2612	$94.26	$94.25	$94.30
Purchase #3	$105.89	13.157%	$119.8219	$119.82	$119.80	$119.80
Purchase #4	$154.51	9.299%	$168.8779	$168.88	$168.90	$168.90
Purchase #5	$162.94	4.149%	$169.7004	$169.70	$169.70	$169.70
Purchase #6	$115.61	11.712%	$129.1502	$129.15	$129.15	$129.20
Purchase #7	$36.46	3.842%	$37.8608	$37.86	$37.85	$37.90
7 purchase totals =	$710.82		$770.2437	$770.24	$770.20	$770.40