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	$190.59	12.184%	$213.8115	$213.81	$213.80	$213.80
Purchase #2	$139.32	8.244%	$150.8055	$150.81	$150.80	$150.80
Purchase #3	$51.51	10.374%	$56.8536	$56.85	$56.85	$56.90
Purchase #4	$92.89	9.760%	$101.9561	$101.96	$101.95	$102.00
Purchase #5	$26.82	4.543%	$28.0384	$28.04	$28.05	$28.00
Purchase #6	$59.38	5.345%	$62.5539	$62.55	$62.55	$62.60
Purchase #7	$33.31	7.232%	$35.719	$35.72	$35.70	$35.70
7 purchase totals =	$593.82		$649.7380	$649.74	$649.70	$649.80