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	$81.26	12.323%	$91.2737	$91.27	$91.25	$91.30
Purchase #2	$197.66	12.533%	$222.4327	$222.43	$222.45	$222.40
Purchase #3	$62.40	12.669%	$70.3055	$70.31	$70.30	$70.30
Purchase #4	$160.32	6.326%	$170.4618	$170.46	$170.45	$170.50
Purchase #5	$94.34	4.817%	$98.8844	$98.88	$98.90	$98.90
Purchase #6	$90.75	10.172%	$99.9811	$99.98	$100.00	$100.00
Purchase #7	$170.73	7.405%	$183.3726	$183.37	$183.35	$183.40
7 purchase totals =	$857.46		$936.7118	$936.70	$936.70	$936.80