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	$78.98	12.786%	$89.0784	$89.08	$89.10	$89.10
Purchase #2	$93.62	3.774%	$97.1532	$97.15	$97.15	$97.20
Purchase #3	$104.46	12.457%	$117.4726	$117.47	$117.45	$117.50
Purchase #4	$152.76	12.265%	$171.496	$171.50	$171.50	$171.50
Purchase #5	$90.32	12.339%	$101.4646	$101.46	$101.45	$101.50
Purchase #6	$228.93	7.596%	$246.3195	$246.32	$246.30	$246.30
Purchase #7	$21.49	6.793%	$22.9498	$22.95	$22.95	$22.90
7 purchase totals =	$770.56		$845.9341	$845.93	$845.90	$846.00