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	$70.84	13.423%	$80.3489	$80.35	$80.35	$80.30
Purchase #2	$223.50	13.717%	$254.1575	$254.16	$254.15	$254.20
Purchase #3	$183.65	6.865%	$196.2576	$196.26	$196.25	$196.30
Purchase #4	$235.26	3.288%	$242.9953	$243.00	$243.00	$243.00
Purchase #5	$89.71	7.387%	$96.3369	$96.34	$96.35	$96.30
Purchase #6	$13.26	7.498%	$14.2542	$14.25	$14.25	$14.30
Purchase #7	$97.56	6.111%	$103.5219	$103.52	$103.50	$103.50
7 purchase totals =	$913.78		$987.8723	$987.88	$987.85	$987.90