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	$159.69	4.731%	$167.2449	$167.24	$167.25	$167.20
Purchase #2	$167.54	13.620%	$190.3589	$190.36	$190.35	$190.40
Purchase #3	$246.98	9.759%	$271.0828	$271.08	$271.10	$271.10
Purchase #4	$30.41	11.463%	$33.8959	$33.90	$33.90	$33.90
Purchase #5	$242.62	13.194%	$274.6313	$274.63	$274.65	$274.60
Purchase #6	$54.58	4.241%	$56.8947	$56.89	$56.90	$56.90
Purchase #7	$203.63	5.817%	$215.4752	$215.48	$215.50	$215.50
7 purchase totals =	$1,105.45		$1,209.5837	$1,209.58	$1,209.65	$1,209.60