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	$248.87	13.275%	$281.9075	$281.91	$281.90	$281.90
Purchase #2	$233.88	12.600%	$263.3489	$263.35	$263.35	$263.30
Purchase #3	$157.93	6.775%	$168.6298	$168.63	$168.65	$168.60
Purchase #4	$38.59	4.538%	$40.3412	$40.34	$40.35	$40.30
Purchase #5	$243.42	11.141%	$270.5394	$270.54	$270.55	$270.50
Purchase #6	$196.89	11.621%	$219.7706	$219.77	$219.75	$219.80
Purchase #7	$99.78	9.199%	$108.9588	$108.96	$108.95	$109.00
7 purchase totals =	$1,219.36		$1,353.4962	$1,353.50	$1,353.50	$1,353.40