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	$88.76	12.257%	$99.6393	$99.64	$99.65	$99.60
Purchase #2	$115.78	10.386%	$127.8049	$127.80	$127.80	$127.80
Purchase #3	$79.40	13.612%	$90.2079	$90.21	$90.20	$90.20
Purchase #4	$153.84	6.798%	$164.298	$164.30	$164.30	$164.30
Purchase #5	$6.79	12.729%	$7.6543	$7.65	$7.65	$7.70
Purchase #6	$78.41	4.135%	$81.6523	$81.65	$81.65	$81.70
Purchase #7	$149.68	12.430%	$168.2852	$168.29	$168.30	$168.30
7 purchase totals =	$672.66		$739.5419	$739.54	$739.55	$739.60