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	$98.48	12.507%	$110.7969	$110.80	$110.80	$110.80
Purchase #2	$226.59	3.132%	$233.6868	$233.69	$233.70	$233.70
Purchase #3	$38.96	8.624%	$42.3199	$42.32	$42.30	$42.30
Purchase #4	$31.91	3.853%	$33.1395	$33.14	$33.15	$33.10
Purchase #5	$40.49	11.342%	$45.0824	$45.08	$45.10	$45.10
Purchase #6	$152.73	10.409%	$168.6277	$168.63	$168.65	$168.60
Purchase #7	$46.32	4.447%	$48.3799	$48.38	$48.40	$48.40
7 purchase totals =	$635.48		$682.0331	$682.04	$682.10	$682.00