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	$26.44	4.365%	$27.5941	$27.59	$27.60	$27.60
Purchase #2	$136.75	3.352%	$141.3339	$141.33	$141.35	$141.30
Purchase #3	$35.85	12.268%	$40.2481	$40.25	$40.25	$40.20
Purchase #4	$54.72	9.456%	$59.8943	$59.89	$59.90	$59.90
Purchase #5	$93.46	6.430%	$99.4695	$99.47	$99.45	$99.50
Purchase #6	$186.78	5.529%	$197.1071	$197.11	$197.10	$197.10
Purchase #7	$224.70	13.386%	$254.7783	$254.78	$254.80	$254.80
7 purchase totals =	$758.70		$820.4253	$820.42	$820.45	$820.40