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	$92.90	9.729%	$101.9382	$101.94	$101.95	$101.90
Purchase #2	$74.53	10.214%	$82.1425	$82.14	$82.15	$82.10
Purchase #3	$221.63	12.147%	$248.5514	$248.55	$248.55	$248.60
Purchase #4	$109.26	4.377%	$114.0423	$114.04	$114.05	$114.00
Purchase #5	$196.38	13.124%	$222.1529	$222.15	$222.15	$222.20
Purchase #6	$193.90	3.560%	$200.8028	$200.80	$200.80	$200.80
Purchase #7	$222.66	3.858%	$231.2502	$231.25	$231.25	$231.30
7 purchase totals =	$1,111.26		$1,200.8803	$1,200.87	$1,200.90	$1,200.90