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	$45.46	3.740%	$47.1602	$47.16	$47.15	$47.20
Purchase #2	$83.42	8.289%	$90.3347	$90.33	$90.35	$90.30
Purchase #3	$72.54	10.174%	$79.9202	$79.92	$79.90	$79.90
Purchase #4	$78.64	4.700%	$82.3361	$82.34	$82.35	$82.30
Purchase #5	$54.45	8.493%	$59.0744	$59.07	$59.05	$59.10
Purchase #6	$75.50	5.362%	$79.5483	$79.55	$79.55	$79.50
Purchase #7	$145.25	7.416%	$156.0217	$156.02	$156.00	$156.00
7 purchase totals =	$555.26		$594.3956	$594.39	$594.35	$594.30