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	$223.87	6.535%	$238.4999	$238.50	$238.50	$238.50
Purchase #2	$200.37	4.459%	$209.3045	$209.30	$209.30	$209.30
Purchase #3	$152.56	4.811%	$159.8997	$159.90	$159.90	$159.90
Purchase #4	$32.58	5.190%	$34.2709	$34.27	$34.25	$34.30
Purchase #5	$182.57	9.701%	$200.2811	$200.28	$200.30	$200.30
Purchase #6	$135.97	10.600%	$150.3828	$150.38	$150.40	$150.40
Purchase #7	$219.97	13.742%	$250.1983	$250.20	$250.20	$250.20
7 purchase totals =	$1,147.89		$1,242.8372	$1,242.83	$1,242.85	$1,242.90