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	$105.69	12.726%	$119.1401	$119.14	$119.15	$119.10
Purchase #2	$248.61	6.413%	$264.5534	$264.55	$264.55	$264.60
Purchase #3	$42.77	11.210%	$47.5645	$47.56	$47.55	$47.60
Purchase #4	$83.98	8.236%	$90.8966	$90.90	$90.90	$90.90
Purchase #5	$8.32	5.560%	$8.7826	$8.78	$8.80	$8.80
Purchase #6	$171.56	7.855%	$185.036	$185.04	$185.05	$185.00
Purchase #7	$120.50	6.486%	$128.3156	$128.32	$128.30	$128.30
7 purchase totals =	$781.43		$844.2888	$844.29	$844.30	$844.30