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	$74.38	12.179%	$83.4387	$83.44	$83.45	$83.40
Purchase #2	$85.96	4.681%	$89.9838	$89.98	$90.00	$90.00
Purchase #3	$21.54	10.602%	$23.8237	$23.82	$23.80	$23.80
Purchase #4	$95.37	13.372%	$108.1229	$108.12	$108.10	$108.10
Purchase #5	$40.37	4.793%	$42.3049	$42.30	$42.30	$42.30
Purchase #6	$98.39	11.814%	$110.0138	$110.01	$110.00	$110.00
Purchase #7	$34.51	8.130%	$37.3157	$37.32	$37.30	$37.30
7 purchase totals =	$450.52		$495.0035	$494.99	$494.95	$494.90