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	$76.71	3.108%	$79.0941	$79.09	$79.10	$79.10
Purchase #2	$146.73	13.391%	$166.3786	$166.38	$166.40	$166.40
Purchase #3	$192.89	12.477%	$216.9569	$216.96	$216.95	$217.00
Purchase #4	$124.55	12.369%	$139.9556	$139.96	$139.95	$140.00
Purchase #5	$215.90	12.269%	$242.3888	$242.39	$242.40	$242.40
Purchase #6	$153.42	9.578%	$168.1146	$168.11	$168.10	$168.10
Purchase #7	$209.86	6.216%	$222.9049	$222.90	$222.90	$222.90
7 purchase totals =	$1,120.06		$1,235.7935	$1,235.79	$1,235.80	$1,235.90