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	$109.41	5.569%	$115.503	$115.50	$115.50	$115.50
Purchase #2	$94.37	11.185%	$104.9253	$104.93	$104.95	$104.90
Purchase #3	$55.80	6.580%	$59.4716	$59.47	$59.45	$59.50
Purchase #4	$24.63	12.516%	$27.7127	$27.71	$27.70	$27.70
Purchase #5	$209.82	13.353%	$237.8373	$237.84	$237.85	$237.80
Purchase #6	$133.70	6.874%	$142.8905	$142.89	$142.90	$142.90
Purchase #7	$197.47	9.651%	$216.5278	$216.53	$216.55	$216.50
7 purchase totals =	$825.20		$904.8682	$904.87	$904.90	$904.80