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	$37.98	7.224%	$40.7237	$40.72	$40.70	$40.70
Purchase #2	$188.92	4.188%	$196.832	$196.83	$196.85	$196.80
Purchase #3	$40.51	8.317%	$43.8792	$43.88	$43.90	$43.90
Purchase #4	$208.91	11.455%	$232.8406	$232.84	$232.85	$232.80
Purchase #5	$106.35	3.693%	$110.2775	$110.28	$110.30	$110.30
Purchase #6	$134.50	13.696%	$152.9211	$152.92	$152.90	$152.90
Purchase #7	$169.59	3.520%	$175.5596	$175.56	$175.55	$175.60
7 purchase totals =	$886.76		$953.0337	$953.03	$953.05	$953.00