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	$66.55	6.109%	$70.6155	$70.62	$70.60	$70.60
Purchase #2	$89.90	12.308%	$100.9649	$100.96	$100.95	$101.00
Purchase #3	$65.59	9.162%	$71.5994	$71.60	$71.60	$71.60
Purchase #4	$75.71	7.292%	$81.2308	$81.23	$81.25	$81.20
Purchase #5	$240.90	9.180%	$263.0146	$263.01	$263.00	$263.00
Purchase #6	$243.44	10.284%	$268.4754	$268.48	$268.50	$268.50
Purchase #7	$82.96	8.666%	$90.1493	$90.15	$90.15	$90.10
7 purchase totals =	$865.05		$946.0499	$946.05	$946.05	$946.00