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	$104.29	9.810%	$114.5208	$114.52	$114.50	$114.50
Purchase #2	$209.81	3.179%	$216.4799	$216.48	$216.50	$216.50
Purchase #3	$37.64	4.557%	$39.3553	$39.36	$39.35	$39.40
Purchase #4	$187.54	9.614%	$205.5701	$205.57	$205.55	$205.60
Purchase #5	$200.43	10.681%	$221.8379	$221.84	$221.85	$221.80
Purchase #6	$84.29	13.142%	$95.3674	$95.37	$95.35	$95.40
Purchase #7	$120.58	6.138%	$127.9812	$127.98	$128.00	$128.00
7 purchase totals =	$944.58		$1,021.1126	$1,021.12	$1,021.10	$1,021.20