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	$191.89	12.334%	$215.5577	$215.56	$215.55	$215.60
Purchase #2	$53.97	12.524%	$60.7292	$60.73	$60.75	$60.70
Purchase #3	$104.42	6.320%	$111.0193	$111.02	$111.00	$111.00
Purchase #4	$159.45	7.146%	$170.8443	$170.84	$170.85	$170.80
Purchase #5	$162.58	4.166%	$169.3531	$169.35	$169.35	$169.40
Purchase #6	$35.48	6.166%	$37.6677	$37.67	$37.65	$37.70
Purchase #7	$236.57	5.839%	$250.3833	$250.38	$250.40	$250.40
7 purchase totals =	$944.36		$1,015.5546	$1,015.55	$1,015.55	$1,015.60