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	$40.48	3.596%	$41.9357	$41.94	$41.95	$41.90
Purchase #2	$211.33	12.729%	$238.2302	$238.23	$238.25	$238.20
Purchase #3	$106.46	13.506%	$120.8385	$120.84	$120.85	$120.80
Purchase #4	$168.43	11.482%	$187.7691	$187.77	$187.75	$187.80
Purchase #5	$40.55	3.509%	$41.9729	$41.97	$41.95	$42.00
Purchase #6	$41.44	10.764%	$45.9006	$45.90	$45.90	$45.90
Purchase #7	$45.95	9.241%	$50.1962	$50.20	$50.20	$50.20
7 purchase totals =	$654.64		$726.8432	$726.85	$726.85	$726.80