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	$192.46	3.567%	$199.325	$199.33	$199.35	$199.30
Purchase #2	$148.55	12.846%	$167.6327	$167.63	$167.65	$167.60
Purchase #3	$148.35	5.459%	$156.4484	$156.45	$156.45	$156.40
Purchase #4	$75.33	4.793%	$78.9406	$78.94	$78.95	$78.90
Purchase #5	$134.73	3.580%	$139.5533	$139.55	$139.55	$139.60
Purchase #6	$184.30	6.158%	$195.6492	$195.65	$195.65	$195.60
Purchase #7	$87.77	12.720%	$98.9343	$98.93	$98.95	$98.90
7 purchase totals =	$971.49		$1,036.4835	$1,036.48	$1,036.55	$1,036.30