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	$130.80	6.398%	$139.1686	$139.17	$139.15	$139.20
Purchase #2	$244.59	9.476%	$267.7673	$267.77	$267.75	$267.80
Purchase #3	$177.48	11.267%	$197.4767	$197.48	$197.50	$197.50
Purchase #4	$168.59	10.158%	$185.7154	$185.72	$185.70	$185.70
Purchase #5	$142.42	6.590%	$151.8055	$151.81	$151.80	$151.80
Purchase #6	$246.83	8.621%	$268.1092	$268.11	$268.10	$268.10
Purchase #7	$82.54	8.519%	$89.5716	$89.57	$89.55	$89.60
7 purchase totals =	$1,193.25		$1,299.6143	$1,299.63	$1,299.55	$1,299.70