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	$80.49	3.197%	$83.0633	$83.06	$83.05	$83.10
Purchase #2	$54.56	8.193%	$59.0301	$59.03	$59.05	$59.00
Purchase #3	$79.48	13.530%	$90.2336	$90.23	$90.25	$90.20
Purchase #4	$221.69	3.229%	$228.8484	$228.85	$228.85	$228.80
Purchase #5	$25.65	4.601%	$26.8302	$26.83	$26.85	$26.80
Purchase #6	$88.65	6.405%	$94.328	$94.33	$94.35	$94.30
Purchase #7	$41.92	12.391%	$47.1143	$47.11	$47.10	$47.10
7 purchase totals =	$592.44		$629.4479	$629.44	$629.50	$629.30