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	$65.35	5.482%	$68.9325	$68.93	$68.95	$68.90
Purchase #2	$106.83	3.740%	$110.8254	$110.83	$110.85	$110.80
Purchase #3	$101.40	13.519%	$115.1083	$115.11	$115.10	$115.10
Purchase #4	$216.51	10.359%	$238.9383	$238.94	$238.95	$238.90
Purchase #5	$243.55	13.570%	$276.5997	$276.60	$276.60	$276.60
Purchase #6	$136.84	10.179%	$150.7689	$150.77	$150.75	$150.80
Purchase #7	$81.97	9.665%	$89.8924	$89.89	$89.90	$89.90
7 purchase totals =	$952.45		$1,051.0655	$1,051.07	$1,051.10	$1,051.00