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	$101.32	8.589%	$110.0224	$110.02	$110.00	$110.00
Purchase #2	$40.97	3.853%	$42.5486	$42.55	$42.55	$42.50
Purchase #3	$168.55	9.464%	$184.5016	$184.50	$184.50	$184.50
Purchase #4	$175.55	3.281%	$181.3098	$181.31	$181.30	$181.30
Purchase #5	$57.81	10.302%	$63.7656	$63.77	$63.75	$63.80
Purchase #6	$101.74	7.134%	$108.9981	$109.00	$109.00	$109.00
Purchase #7	$67.89	7.212%	$72.7862	$72.79	$72.80	$72.80
7 purchase totals =	$713.83		$763.9323	$763.94	$763.90	$763.90