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	$175.79	9.172%	$191.9135	$191.91	$191.90	$191.90
Purchase #2	$137.29	6.588%	$146.3347	$146.33	$146.35	$146.30
Purchase #3	$205.48	8.601%	$223.1533	$223.15	$223.15	$223.20
Purchase #4	$186.53	6.287%	$198.2571	$198.26	$198.25	$198.30
Purchase #5	$122.86	12.750%	$138.5247	$138.52	$138.50	$138.50
Purchase #6	$79.50	3.161%	$82.013	$82.01	$82.00	$82.00
Purchase #7	$5.41	3.279%	$5.5874	$5.59	$5.60	$5.60
7 purchase totals =	$912.86		$985.7837	$985.77	$985.75	$985.80