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	$182.42	11.281%	$202.9988	$203.00	$203.00	$203.00
Purchase #2	$133.46	10.217%	$147.0956	$147.10	$147.10	$147.10
Purchase #3	$160.33	3.623%	$166.1388	$166.14	$166.15	$166.10
Purchase #4	$116.35	12.628%	$131.0427	$131.04	$131.05	$131.00
Purchase #5	$21.70	9.707%	$23.8064	$23.81	$23.80	$23.80
Purchase #6	$55.79	7.393%	$59.9146	$59.91	$59.90	$59.90
Purchase #7	$79.84	12.435%	$89.7681	$89.77	$89.75	$89.80
7 purchase totals =	$749.89		$820.7650	$820.77	$820.75	$820.70