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	$40.39	12.819%	$45.5676	$45.57	$45.55	$45.60
Purchase #2	$135.53	5.315%	$142.7334	$142.73	$142.75	$142.70
Purchase #3	$156.78	7.756%	$168.9399	$168.94	$168.95	$168.90
Purchase #4	$104.44	10.479%	$115.3843	$115.38	$115.40	$115.40
Purchase #5	$20.61	6.238%	$21.8957	$21.90	$21.90	$21.90
Purchase #6	$181.60	9.755%	$199.3151	$199.32	$199.30	$199.30
Purchase #7	$170.29	11.522%	$189.9108	$189.91	$189.90	$189.90
7 purchase totals =	$809.64		$883.7468	$883.75	$883.75	$883.70