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	$23.95	7.343%	$25.7086	$25.71	$25.70	$25.70
Purchase #2	$147.50	11.639%	$164.6675	$164.67	$164.65	$164.70
Purchase #3	$30.29	5.849%	$32.0617	$32.06	$32.05	$32.10
Purchase #4	$82.47	9.119%	$89.9904	$89.99	$90.00	$90.00
Purchase #5	$83.53	13.148%	$94.5125	$94.51	$94.50	$94.50
Purchase #6	$58.51	3.107%	$60.3279	$60.33	$60.35	$60.30
Purchase #7	$116.34	5.755%	$123.0354	$123.04	$123.05	$123.00
7 purchase totals =	$542.59		$590.3040	$590.31	$590.30	$590.30