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	$131.91	4.230%	$137.4898	$137.49	$137.50	$137.50
Purchase #2	$166.54	11.300%	$185.359	$185.36	$185.35	$185.40
Purchase #3	$248.95	4.630%	$260.4764	$260.48	$260.50	$260.50
Purchase #4	$103.81	7.330%	$111.4193	$111.42	$111.40	$111.40
Purchase #5	$158.68	4.874%	$166.4141	$166.41	$166.40	$166.40
Purchase #6	$162.43	4.359%	$169.5103	$169.51	$169.50	$169.50
Purchase #7	$121.55	11.802%	$135.8953	$135.90	$135.90	$135.90
7 purchase totals =	$1,093.87		$1,166.5642	$1,166.57	$1,166.55	$1,166.60