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	$81.92	10.824%	$90.787	$90.79	$90.80	$90.80
Purchase #2	$140.48	11.852%	$157.1297	$157.13	$157.15	$157.10
Purchase #3	$189.41	5.133%	$199.1324	$199.13	$199.15	$199.10
Purchase #4	$250.82	7.375%	$269.318	$269.32	$269.30	$269.30
Purchase #5	$18.72	10.497%	$20.685	$20.69	$20.70	$20.70
Purchase #6	$195.46	6.705%	$208.5656	$208.57	$208.55	$208.60
Purchase #7	$53.75	7.846%	$57.9672	$57.97	$57.95	$58.00
7 purchase totals =	$930.56		$1,003.5849	$1,003.60	$1,003.60	$1,003.60