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	$122.92	13.421%	$139.4171	$139.42	$139.40	$139.40
Purchase #2	$20.61	9.316%	$22.53	$22.53	$22.55	$22.50
Purchase #3	$190.32	6.344%	$202.3939	$202.39	$202.40	$202.40
Purchase #4	$64.81	11.596%	$72.3254	$72.33	$72.35	$72.30
Purchase #5	$83.76	7.319%	$89.8904	$89.89	$89.90	$89.90
Purchase #6	$36.69	8.241%	$39.7136	$39.71	$39.70	$39.70
Purchase #7	$79.88	7.496%	$85.8678	$85.87	$85.85	$85.90
7 purchase totals =	$598.99		$652.1382	$652.14	$652.15	$652.10