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	$85.63	3.315%	$88.4686	$88.47	$88.45	$88.50
Purchase #2	$71.96	11.323%	$80.108	$80.11	$80.10	$80.10
Purchase #3	$94.29	10.476%	$104.1678	$104.17	$104.15	$104.20
Purchase #4	$218.79	10.804%	$242.4281	$242.43	$242.45	$242.40
Purchase #5	$139.51	11.143%	$155.0556	$155.06	$155.05	$155.10
Purchase #6	$132.58	3.742%	$137.5411	$137.54	$137.55	$137.50
Purchase #7	$200.79	5.736%	$212.3073	$212.31	$212.30	$212.30
7 purchase totals =	$943.55		$1,020.0765	$1,020.09	$1,020.05	$1,020.10