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	$96.33	3.834%	$100.0233	$100.02	$100.00	$100.00
Purchase #2	$152.32	12.853%	$171.8977	$171.90	$171.90	$171.90
Purchase #3	$95.85	5.540%	$101.1601	$101.16	$101.15	$101.20
Purchase #4	$160.82	13.704%	$182.8588	$182.86	$182.85	$182.90
Purchase #5	$100.43	8.571%	$109.0379	$109.04	$109.05	$109.00
Purchase #6	$197.62	12.356%	$222.0379	$222.04	$222.05	$222.00
Purchase #7	$71.76	13.447%	$81.4096	$81.41	$81.40	$81.40
7 purchase totals =	$875.13		$968.4253	$968.43	$968.40	$968.40