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	$203.51	13.767%	$231.5272	$231.53	$231.55	$231.50
Purchase #2	$200.74	12.179%	$225.1881	$225.19	$225.20	$225.20
Purchase #3	$165.95	12.143%	$186.1013	$186.10	$186.10	$186.10
Purchase #4	$174.43	6.543%	$185.843	$185.84	$185.85	$185.80
Purchase #5	$52.85	12.259%	$59.3289	$59.33	$59.35	$59.30
Purchase #6	$194.76	13.549%	$221.148	$221.15	$221.15	$221.10
Purchase #7	$128.90	10.868%	$142.9089	$142.91	$142.90	$142.90
7 purchase totals =	$1,121.14		$1,252.0454	$1,252.05	$1,252.10	$1,251.90