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	$27.49	4.661%	$28.7713	$28.77	$28.75	$28.80
Purchase #2	$247.86	4.234%	$258.3544	$258.35	$258.35	$258.40
Purchase #3	$146.86	7.566%	$157.9714	$157.97	$157.95	$158.00
Purchase #4	$68.85	4.540%	$71.9758	$71.98	$72.00	$72.00
Purchase #5	$30.96	4.529%	$32.3622	$32.36	$32.35	$32.40
Purchase #6	$57.59	3.726%	$59.7358	$59.74	$59.75	$59.70
Purchase #7	$144.91	3.740%	$150.3296	$150.33	$150.35	$150.30
7 purchase totals =	$724.52		$759.5005	$759.50	$759.50	$759.60