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	$149.44	12.760%	$168.5085	$168.51	$168.50	$168.50
Purchase #2	$108.37	6.653%	$115.5799	$115.58	$115.60	$115.60
Purchase #3	$36.33	10.280%	$40.0647	$40.06	$40.05	$40.10
Purchase #4	$66.26	11.300%	$73.7474	$73.75	$73.75	$73.70
Purchase #5	$67.47	7.438%	$72.4884	$72.49	$72.50	$72.50
Purchase #6	$85.80	7.114%	$91.9038	$91.90	$91.90	$91.90
Purchase #7	$11.64	9.221%	$12.7133	$12.71	$12.70	$12.70
7 purchase totals =	$525.31		$575.0060	$575.00	$575.00	$575.00