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	$247.57	10.276%	$273.0103	$273.01	$273.00	$273.00
Purchase #2	$68.63	6.166%	$72.8617	$72.86	$72.85	$72.90
Purchase #3	$205.97	9.192%	$224.9028	$224.90	$224.90	$224.90
Purchase #4	$72.45	7.594%	$77.9519	$77.95	$77.95	$78.00
Purchase #5	$227.59	11.221%	$253.1279	$253.13	$253.15	$253.10
Purchase #6	$234.56	6.599%	$250.0386	$250.04	$250.05	$250.00
Purchase #7	$166.27	9.796%	$182.5578	$182.56	$182.55	$182.60
7 purchase totals =	$1,223.04		$1,334.4510	$1,334.45	$1,334.45	$1,334.50