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	$171.89	10.427%	$189.813	$189.81	$189.80	$189.80
Purchase #2	$12.33	8.459%	$13.373	$13.37	$13.35	$13.40
Purchase #3	$74.46	10.303%	$82.1316	$82.13	$82.15	$82.10
Purchase #4	$201.74	4.872%	$211.5688	$211.57	$211.55	$211.60
Purchase #5	$223.25	9.187%	$243.76	$243.76	$243.75	$243.80
Purchase #6	$70.31	10.158%	$77.4521	$77.45	$77.45	$77.50
Purchase #7	$69.58	13.469%	$78.9517	$78.95	$78.95	$79.00
7 purchase totals =	$823.56		$897.0502	$897.04	$897.00	$897.20