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	$40.66	4.337%	$42.4234	$42.42	$42.40	$42.40
Purchase #2	$157.30	4.300%	$164.0639	$164.06	$164.05	$164.10
Purchase #3	$180.89	8.299%	$195.9021	$195.90	$195.90	$195.90
Purchase #4	$73.43	9.507%	$80.411	$80.41	$80.40	$80.40
Purchase #5	$196.74	7.429%	$211.3558	$211.36	$211.35	$211.40
Purchase #6	$237.73	11.398%	$264.8265	$264.83	$264.85	$264.80
Purchase #7	$124.58	8.143%	$134.7245	$134.72	$134.70	$134.70
7 purchase totals =	$1,011.33		$1,093.7072	$1,093.70	$1,093.65	$1,093.70