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	$237.90	6.507%	$253.3802	$253.38	$253.40	$253.40
Purchase #2	$135.38	11.428%	$150.8512	$150.85	$150.85	$150.90
Purchase #3	$163.70	13.868%	$186.4019	$186.40	$186.40	$186.40
Purchase #4	$204.86	9.209%	$223.7256	$223.73	$223.75	$223.70
Purchase #5	$105.45	6.240%	$112.0301	$112.03	$112.05	$112.00
Purchase #6	$59.53	9.682%	$65.2937	$65.29	$65.30	$65.30
Purchase #7	$143.71	13.165%	$162.6294	$162.63	$162.65	$162.60
7 purchase totals =	$1,050.53		$1,154.3121	$1,154.31	$1,154.40	$1,154.30