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	$129.85	5.512%	$137.0073	$137.01	$137.00	$137.00
Purchase #2	$29.67	4.764%	$31.0835	$31.08	$31.10	$31.10
Purchase #3	$36.31	10.741%	$40.2101	$40.21	$40.20	$40.20
Purchase #4	$203.47	9.238%	$222.2666	$222.27	$222.25	$222.30
Purchase #5	$120.85	11.675%	$134.9592	$134.96	$134.95	$135.00
Purchase #6	$250.73	13.439%	$284.4256	$284.43	$284.45	$284.40
Purchase #7	$153.63	11.597%	$171.4465	$171.45	$171.45	$171.40
7 purchase totals =	$924.51		$1,021.3988	$1,021.41	$1,021.40	$1,021.40