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	$80.40	10.802%	$89.0848	$89.08	$89.10	$89.10
Purchase #2	$237.38	9.701%	$260.4082	$260.41	$260.40	$260.40
Purchase #3	$69.57	11.421%	$77.5156	$77.52	$77.50	$77.50
Purchase #4	$50.69	11.637%	$56.5888	$56.59	$56.60	$56.60
Purchase #5	$79.74	9.755%	$87.5186	$87.52	$87.50	$87.50
Purchase #6	$36.53	4.691%	$38.2436	$38.24	$38.25	$38.20
Purchase #7	$31.61	12.473%	$35.5527	$35.55	$35.55	$35.60
7 purchase totals =	$585.92		$644.9123	$644.91	$644.90	$644.90