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	$135.94	7.627%	$146.3081	$146.31	$146.30	$146.30
Purchase #2	$233.27	4.547%	$243.8768	$243.88	$243.90	$243.90
Purchase #3	$95.54	12.740%	$107.7118	$107.71	$107.70	$107.70
Purchase #4	$12.98	13.859%	$14.7789	$14.78	$14.80	$14.80
Purchase #5	$90.89	10.820%	$100.7243	$100.72	$100.70	$100.70
Purchase #6	$148.55	10.642%	$164.3587	$164.36	$164.35	$164.40
Purchase #7	$185.26	7.594%	$199.3286	$199.33	$199.35	$199.30
7 purchase totals =	$902.43		$977.0872	$977.09	$977.10	$977.10