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	$71.91	11.569%	$80.2293	$80.23	$80.25	$80.20
Purchase #2	$76.40	10.871%	$84.7054	$84.71	$84.70	$84.70
Purchase #3	$186.54	3.180%	$192.472	$192.47	$192.45	$192.50
Purchase #4	$38.81	9.521%	$42.5051	$42.51	$42.50	$42.50
Purchase #5	$165.52	9.310%	$180.9299	$180.93	$180.95	$180.90
Purchase #6	$144.48	8.612%	$156.9226	$156.92	$156.90	$156.90
Purchase #7	$239.80	13.568%	$272.3361	$272.34	$272.35	$272.30
7 purchase totals =	$923.46		$1,010.1004	$1,010.11	$1,010.10	$1,010.00