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	$181.73	4.557%	$190.0114	$190.01	$190.00	$190.00
Purchase #2	$39.85	6.339%	$42.3761	$42.38	$42.40	$42.40
Purchase #3	$84.71	5.192%	$89.1081	$89.11	$89.10	$89.10
Purchase #4	$211.43	11.349%	$235.4252	$235.43	$235.45	$235.40
Purchase #5	$77.69	3.709%	$80.5715	$80.57	$80.55	$80.60
Purchase #6	$178.37	13.259%	$202.0201	$202.02	$202.00	$202.00
Purchase #7	$25.90	11.653%	$28.9181	$28.92	$28.90	$28.90
7 purchase totals =	$799.68		$868.4305	$868.44	$868.40	$868.40