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	$81.65	3.182%	$84.2481	$84.25	$84.25	$84.20
Purchase #2	$39.62	8.143%	$42.8463	$42.85	$42.85	$42.80
Purchase #3	$137.57	9.432%	$150.5456	$150.55	$150.55	$150.50
Purchase #4	$201.73	8.604%	$219.0868	$219.09	$219.10	$219.10
Purchase #5	$84.78	13.633%	$96.3381	$96.34	$96.35	$96.30
Purchase #6	$72.63	13.235%	$82.2426	$82.24	$82.25	$82.20
Purchase #7	$87.89	13.309%	$99.5873	$99.59	$99.60	$99.60
7 purchase totals =	$705.87		$774.8948	$774.91	$774.95	$774.70