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	$83.84	6.812%	$89.5512	$89.55	$89.55	$89.60
Purchase #2	$41.85	10.779%	$46.361	$46.36	$46.35	$46.40
Purchase #3	$64.55	10.798%	$71.5201	$71.52	$71.50	$71.50
Purchase #4	$243.41	11.270%	$270.8423	$270.84	$270.85	$270.80
Purchase #5	$27.29	4.306%	$28.4651	$28.47	$28.45	$28.50
Purchase #6	$238.34	8.164%	$257.7981	$257.80	$257.80	$257.80
Purchase #7	$202.96	13.249%	$229.8502	$229.85	$229.85	$229.90
7 purchase totals =	$902.24		$994.3880	$994.39	$994.35	$994.50