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	$149.77	12.539%	$168.5497	$168.55	$168.55	$168.50
Purchase #2	$228.73	8.815%	$248.8925	$248.89	$248.90	$248.90
Purchase #3	$66.35	7.870%	$71.5717	$71.57	$71.55	$71.60
Purchase #4	$106.36	4.171%	$110.7963	$110.80	$110.80	$110.80
Purchase #5	$96.55	13.358%	$109.4471	$109.45	$109.45	$109.40
Purchase #6	$101.46	4.848%	$106.3788	$106.38	$106.40	$106.40
Purchase #7	$50.26	9.250%	$54.9091	$54.91	$54.90	$54.90
7 purchase totals =	$799.48		$870.5452	$870.55	$870.55	$870.50