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	$146.68	8.772%	$159.5468	$159.55	$159.55	$159.50
Purchase #2	$162.88	5.702%	$172.1674	$172.17	$172.15	$172.20
Purchase #3	$237.71	13.809%	$270.5354	$270.54	$270.55	$270.50
Purchase #4	$24.76	6.352%	$26.3328	$26.33	$26.35	$26.30
Purchase #5	$141.84	7.736%	$152.8127	$152.81	$152.80	$152.80
Purchase #6	$250.46	7.404%	$269.0041	$269.00	$269.00	$269.00
Purchase #7	$85.69	5.697%	$90.5718	$90.57	$90.55	$90.60
7 purchase totals =	$1,050.02		$1,140.9710	$1,140.97	$1,140.95	$1,140.90