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	$63.89	12.544%	$71.9044	$71.90	$71.90	$71.90
Purchase #2	$125.76	4.592%	$131.5349	$131.53	$131.55	$131.50
Purchase #3	$135.31	7.234%	$145.0983	$145.10	$145.10	$145.10
Purchase #4	$91.40	8.391%	$99.0694	$99.07	$99.05	$99.10
Purchase #5	$80.52	4.297%	$83.9799	$83.98	$84.00	$84.00
Purchase #6	$174.56	13.398%	$197.9475	$197.95	$197.95	$197.90
Purchase #7	$129.32	12.828%	$145.9092	$145.91	$145.90	$145.90
7 purchase totals =	$800.76		$875.4436	$875.44	$875.45	$875.40