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	$106.85	6.290%	$113.5709	$113.57	$113.55	$113.60
Purchase #2	$137.59	10.842%	$152.5075	$152.51	$152.50	$152.50
Purchase #3	$90.79	10.501%	$100.3239	$100.32	$100.30	$100.30
Purchase #4	$150.59	6.391%	$160.2142	$160.21	$160.20	$160.20
Purchase #5	$171.76	13.746%	$195.3701	$195.37	$195.35	$195.40
Purchase #6	$82.74	8.258%	$89.5727	$89.57	$89.55	$89.60
Purchase #7	$83.55	9.696%	$91.651	$91.65	$91.65	$91.70
7 purchase totals =	$823.87		$903.2103	$903.20	$903.10	$903.30