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	$44.48	13.174%	$50.3398	$50.34	$50.35	$50.30
Purchase #2	$81.57	9.162%	$89.0434	$89.04	$89.05	$89.00
Purchase #3	$165.63	12.155%	$185.7623	$185.76	$185.75	$185.80
Purchase #4	$5.88	11.614%	$6.5629	$6.56	$6.55	$6.60
Purchase #5	$98.88	11.215%	$109.9694	$109.97	$109.95	$110.00
Purchase #6	$7.45	5.710%	$7.8754	$7.88	$7.90	$7.90
Purchase #7	$147.55	10.569%	$163.1446	$163.14	$163.15	$163.10
7 purchase totals =	$551.44		$612.6978	$612.69	$612.70	$612.70