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	$166.30	8.694%	$180.7581	$180.76	$180.75	$180.80
Purchase #2	$209.43	13.850%	$238.4361	$238.44	$238.45	$238.40
Purchase #3	$81.60	10.181%	$89.9077	$89.91	$89.90	$89.90
Purchase #4	$184.97	8.637%	$200.9459	$200.95	$200.95	$200.90
Purchase #5	$205.57	12.662%	$231.5993	$231.60	$231.60	$231.60
Purchase #6	$119.63	4.809%	$125.383	$125.38	$125.40	$125.40
Purchase #7	$154.73	7.570%	$166.4431	$166.44	$166.45	$166.40
7 purchase totals =	$1,122.23		$1,233.4732	$1,233.48	$1,233.50	$1,233.40