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	$40.80	12.505%	$45.902	$45.90	$45.90	$45.90
Purchase #2	$215.34	3.399%	$222.6594	$222.66	$222.65	$222.70
Purchase #3	$75.86	8.730%	$82.4826	$82.48	$82.50	$82.50
Purchase #4	$125.43	8.536%	$136.1367	$136.14	$136.15	$136.10
Purchase #5	$247.28	10.517%	$273.2864	$273.29	$273.30	$273.30
Purchase #6	$150.36	12.319%	$168.8828	$168.88	$168.90	$168.90
Purchase #7	$178.78	8.182%	$193.4078	$193.41	$193.40	$193.40
7 purchase totals =	$1,033.85		$1,122.7577	$1,122.76	$1,122.80	$1,122.80