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	$99.54	9.257%	$108.7544	$108.75	$108.75	$108.80
Purchase #2	$73.74	13.726%	$83.8616	$83.86	$83.85	$83.90
Purchase #3	$235.86	8.224%	$255.2571	$255.26	$255.25	$255.30
Purchase #4	$221.34	3.479%	$229.0404	$229.04	$229.05	$229.00
Purchase #5	$69.31	4.589%	$72.4906	$72.49	$72.50	$72.50
Purchase #6	$221.69	3.270%	$228.9393	$228.94	$228.95	$228.90
Purchase #7	$64.35	11.693%	$71.8744	$71.87	$71.85	$71.90
7 purchase totals =	$985.83		$1,050.2178	$1,050.21	$1,050.20	$1,050.30