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	$225.64	12.303%	$253.4005	$253.40	$253.40	$253.40
Purchase #2	$33.43	13.123%	$37.817	$37.82	$37.80	$37.80
Purchase #3	$212.50	13.216%	$240.584	$240.58	$240.60	$240.60
Purchase #4	$189.39	9.270%	$206.9465	$206.95	$206.95	$206.90
Purchase #5	$109.61	9.779%	$120.3288	$120.33	$120.35	$120.30
Purchase #6	$28.54	9.667%	$31.299	$31.30	$31.30	$31.30
Purchase #7	$177.77	7.291%	$190.7312	$190.73	$190.75	$190.70
7 purchase totals =	$976.88		$1,081.1070	$1,081.11	$1,081.15	$1,081.00