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	$94.97	6.125%	$100.7869	$100.79	$100.80	$100.80
Purchase #2	$42.57	9.310%	$46.5333	$46.53	$46.55	$46.50
Purchase #3	$10.47	9.540%	$11.4688	$11.47	$11.45	$11.50
Purchase #4	$101.83	12.593%	$114.6535	$114.65	$114.65	$114.70
Purchase #5	$53.33	10.862%	$59.1227	$59.12	$59.10	$59.10
Purchase #6	$103.30	6.737%	$110.2593	$110.26	$110.25	$110.30
Purchase #7	$52.46	13.706%	$59.6502	$59.65	$59.65	$59.70
7 purchase totals =	$458.93		$502.4747	$502.47	$502.45	$502.60