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	$115.63	13.704%	$131.4759	$131.48	$131.50	$131.50
Purchase #2	$89.66	4.606%	$93.7897	$93.79	$93.80	$93.80
Purchase #3	$25.58	6.443%	$27.2281	$27.23	$27.25	$27.20
Purchase #4	$190.33	10.698%	$210.6915	$210.69	$210.70	$210.70
Purchase #5	$63.65	5.755%	$67.3131	$67.31	$67.30	$67.30
Purchase #6	$196.28	7.751%	$211.4937	$211.49	$211.50	$211.50
Purchase #7	$241.57	12.268%	$271.2058	$271.21	$271.20	$271.20
7 purchase totals =	$922.70		$1,013.1978	$1,013.20	$1,013.25	$1,013.20