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	$141.98	6.618%	$151.3762	$151.38	$151.40	$151.40
Purchase #2	$80.66	11.751%	$90.1384	$90.14	$90.15	$90.10
Purchase #3	$147.74	13.515%	$167.7071	$167.71	$167.70	$167.70
Purchase #4	$54.76	5.594%	$57.8233	$57.82	$57.80	$57.80
Purchase #5	$217.59	9.624%	$238.5309	$238.53	$238.55	$238.50
Purchase #6	$77.75	9.173%	$84.882	$84.88	$84.90	$84.90
Purchase #7	$45.57	3.183%	$47.0205	$47.02	$47.00	$47.00
7 purchase totals =	$766.05		$837.4784	$837.48	$837.50	$837.40