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	$135.39	12.612%	$152.4654	$152.47	$152.45	$152.50
Purchase #2	$128.59	9.857%	$141.2651	$141.27	$141.25	$141.30
Purchase #3	$130.88	11.816%	$146.3448	$146.34	$146.35	$146.30
Purchase #4	$72.27	6.543%	$76.9986	$77.00	$77.00	$77.00
Purchase #5	$115.90	13.764%	$131.8525	$131.85	$131.85	$131.90
Purchase #6	$65.58	8.762%	$71.3261	$71.33	$71.35	$71.30
Purchase #7	$73.79	6.124%	$78.3089	$78.31	$78.30	$78.30
7 purchase totals =	$722.40		$798.5614	$798.57	$798.55	$798.60