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	$51.69	4.717%	$54.1282	$54.13	$54.15	$54.10
Purchase #2	$145.53	7.503%	$156.4491	$156.45	$156.45	$156.40
Purchase #3	$152.43	12.480%	$171.4533	$171.45	$171.45	$171.50
Purchase #4	$50.52	5.403%	$53.2496	$53.25	$53.25	$53.20
Purchase #5	$168.36	6.513%	$179.3253	$179.33	$179.35	$179.30
Purchase #6	$182.94	4.108%	$190.4552	$190.46	$190.45	$190.50
Purchase #7	$29.33	8.126%	$31.7134	$31.71	$31.70	$31.70
7 purchase totals =	$780.80		$836.7741	$836.78	$836.80	$836.70