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	$81.85	10.236%	$90.2282	$90.23	$90.25	$90.20
Purchase #2	$16.28	11.474%	$18.148	$18.15	$18.15	$18.10
Purchase #3	$38.82	8.738%	$42.2121	$42.21	$42.20	$42.20
Purchase #4	$187.75	9.593%	$205.7609	$205.76	$205.75	$205.80
Purchase #5	$102.74	10.264%	$113.2852	$113.29	$113.30	$113.30
Purchase #6	$35.48	13.869%	$40.4007	$40.40	$40.40	$40.40
Purchase #7	$39.63	3.417%	$40.9842	$40.98	$41.00	$41.00
7 purchase totals =	$502.55		$551.0193	$551.02	$551.05	$551.00