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	$156.27	7.347%	$167.7512	$167.75	$167.75	$167.80
Purchase #2	$202.69	9.237%	$221.4125	$221.41	$221.40	$221.40
Purchase #3	$28.34	5.500%	$29.8987	$29.90	$29.90	$29.90
Purchase #4	$86.29	12.107%	$96.7371	$96.74	$96.75	$96.70
Purchase #5	$78.45	8.558%	$85.1638	$85.16	$85.15	$85.20
Purchase #6	$46.74	12.722%	$52.6863	$52.69	$52.70	$52.70
Purchase #7	$84.37	6.421%	$89.7874	$89.79	$89.80	$89.80
7 purchase totals =	$683.15		$743.4370	$743.44	$743.45	$743.50