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	$40.77	4.630%	$42.6577	$42.66	$42.65	$42.70
Purchase #2	$134.30	12.441%	$151.0083	$151.01	$151.00	$151.00
Purchase #3	$223.47	6.586%	$238.1877	$238.19	$238.20	$238.20
Purchase #4	$84.60	6.270%	$89.9044	$89.90	$89.90	$89.90
Purchase #5	$211.59	11.692%	$236.3291	$236.33	$236.35	$236.30
Purchase #6	$204.90	10.493%	$226.4002	$226.40	$226.40	$226.40
Purchase #7	$81.55	10.780%	$90.3411	$90.34	$90.35	$90.30
7 purchase totals =	$981.18		$1,074.8285	$1,074.83	$1,074.85	$1,074.80