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	$29.94	5.154%	$31.4831	$31.48	$31.50	$31.50
Purchase #2	$189.94	11.506%	$211.7945	$211.79	$211.80	$211.80
Purchase #3	$74.33	5.516%	$78.43	$78.43	$78.45	$78.40
Purchase #4	$185.77	12.727%	$209.4129	$209.41	$209.40	$209.40
Purchase #5	$75.61	9.745%	$82.9782	$82.98	$83.00	$83.00
Purchase #6	$64.66	9.767%	$70.9753	$70.98	$71.00	$71.00
Purchase #7	$7.83	3.390%	$8.0954	$8.10	$8.10	$8.10
7 purchase totals =	$628.08		$693.1694	$693.17	$693.25	$693.20