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	$55.36	8.168%	$59.8818	$59.88	$59.90	$59.90
Purchase #2	$224.51	9.623%	$246.1146	$246.11	$246.10	$246.10
Purchase #3	$130.74	12.805%	$147.4813	$147.48	$147.50	$147.50
Purchase #4	$123.69	9.811%	$135.8252	$135.83	$135.85	$135.80
Purchase #5	$227.53	12.477%	$255.9189	$255.92	$255.90	$255.90
Purchase #6	$146.98	9.409%	$160.8093	$160.81	$160.80	$160.80
Purchase #7	$130.55	7.104%	$139.8243	$139.82	$139.80	$139.80
7 purchase totals =	$1,039.36		$1,145.8554	$1,145.85	$1,145.85	$1,145.80