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	$55.46	6.375%	$58.9956	$59.00	$59.00	$59.00
Purchase #2	$84.56	6.671%	$90.201	$90.20	$90.20	$90.20
Purchase #3	$165.85	9.181%	$181.0767	$181.08	$181.10	$181.10
Purchase #4	$40.53	4.833%	$42.4888	$42.49	$42.50	$42.50
Purchase #5	$42.43	4.238%	$44.2282	$44.23	$44.25	$44.20
Purchase #6	$194.94	9.320%	$213.1084	$213.11	$213.10	$213.10
Purchase #7	$209.73	6.855%	$224.107	$224.11	$224.10	$224.10
7 purchase totals =	$793.50		$854.2057	$854.22	$854.25	$854.20