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	$87.78	13.399%	$99.5416	$99.54	$99.55	$99.50
Purchase #2	$250.61	4.113%	$260.9176	$260.92	$260.90	$260.90
Purchase #3	$206.55	13.518%	$234.4714	$234.47	$234.45	$234.50
Purchase #4	$243.69	6.782%	$260.2171	$260.22	$260.20	$260.20
Purchase #5	$78.73	4.401%	$82.1949	$82.19	$82.20	$82.20
Purchase #6	$211.45	12.646%	$238.19	$238.19	$238.20	$238.20
Purchase #7	$137.34	13.349%	$155.6735	$155.67	$155.65	$155.70
7 purchase totals =	$1,216.15		$1,331.2061	$1,331.20	$1,331.15	$1,331.20