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	$31.51	12.684%	$35.5067	$35.51	$35.50	$35.50
Purchase #2	$142.86	13.849%	$162.6447	$162.64	$162.65	$162.60
Purchase #3	$7.42	6.483%	$7.901	$7.90	$7.90	$7.90
Purchase #4	$120.49	12.138%	$135.1151	$135.12	$135.10	$135.10
Purchase #5	$233.91	4.863%	$245.285	$245.29	$245.30	$245.30
Purchase #6	$202.45	13.360%	$229.4973	$229.50	$229.50	$229.50
Purchase #7	$143.74	12.783%	$162.1143	$162.11	$162.10	$162.10
7 purchase totals =	$882.38		$978.0641	$978.07	$978.05	$978.00