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	$70.61	9.308%	$77.1824	$77.18	$77.20	$77.20
Purchase #2	$195.39	13.488%	$221.7442	$221.74	$221.75	$221.70
Purchase #3	$167.48	12.776%	$188.8772	$188.88	$188.90	$188.90
Purchase #4	$33.58	13.582%	$38.1408	$38.14	$38.15	$38.10
Purchase #5	$69.89	11.618%	$78.0098	$78.01	$78.00	$78.00
Purchase #6	$124.52	12.286%	$139.8185	$139.82	$139.80	$139.80
Purchase #7	$225.53	7.364%	$242.138	$242.14	$242.15	$242.10
7 purchase totals =	$887.00		$985.9109	$985.91	$985.95	$985.80