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	$70.86	13.683%	$80.5558	$80.56	$80.55	$80.60
Purchase #2	$27.36	12.867%	$30.8804	$30.88	$30.90	$30.90
Purchase #3	$179.33	10.748%	$198.6044	$198.60	$198.60	$198.60
Purchase #4	$6.43	5.417%	$6.7783	$6.78	$6.80	$6.80
Purchase #5	$147.71	11.353%	$164.4795	$164.48	$164.50	$164.50
Purchase #6	$130.43	9.593%	$142.9421	$142.94	$142.95	$142.90
Purchase #7	$150.89	9.392%	$165.0616	$165.06	$165.05	$165.10
7 purchase totals =	$713.01		$789.3021	$789.30	$789.35	$789.40