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	$104.55	13.182%	$118.3318	$118.33	$118.35	$118.30
Purchase #2	$73.78	11.782%	$82.4728	$82.47	$82.45	$82.50
Purchase #3	$124.28	12.841%	$140.2388	$140.24	$140.25	$140.20
Purchase #4	$68.59	6.364%	$72.9551	$72.96	$72.95	$73.00
Purchase #5	$218.37	11.459%	$243.393	$243.39	$243.40	$243.40
Purchase #6	$234.71	3.284%	$242.4179	$242.42	$242.40	$242.40
Purchase #7	$110.85	4.253%	$115.5645	$115.56	$115.55	$115.60
7 purchase totals =	$935.13		$1,015.3739	$1,015.37	$1,015.35	$1,015.40