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	$80.91	6.700%	$86.331	$86.33	$86.35	$86.30
Purchase #2	$232.38	9.632%	$254.7628	$254.76	$254.75	$254.80
Purchase #3	$38.82	4.165%	$40.4369	$40.44	$40.45	$40.40
Purchase #4	$236.97	13.166%	$268.1695	$268.17	$268.15	$268.20
Purchase #5	$91.60	12.501%	$103.0509	$103.05	$103.05	$103.10
Purchase #6	$160.37	5.737%	$169.5704	$169.57	$169.55	$169.60
Purchase #7	$88.38	9.625%	$96.8866	$96.89	$96.90	$96.90
7 purchase totals =	$929.43		$1,019.2081	$1,019.21	$1,019.20	$1,019.30