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	$150.51	12.568%	$169.4261	$169.43	$169.45	$169.40
Purchase #2	$131.99	12.237%	$148.1416	$148.14	$148.15	$148.10
Purchase #3	$166.73	12.164%	$187.011	$187.01	$187.00	$187.00
Purchase #4	$181.71	9.436%	$198.8562	$198.86	$198.85	$198.90
Purchase #5	$203.94	3.625%	$211.3328	$211.33	$211.35	$211.30
Purchase #6	$55.89	9.790%	$61.3616	$61.36	$61.35	$61.40
Purchase #7	$36.38	12.547%	$40.9446	$40.94	$40.95	$40.90
7 purchase totals =	$927.15		$1,017.0739	$1,017.07	$1,017.10	$1,017.00