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	$170.58	3.436%	$176.4411	$176.44	$176.45	$176.40
Purchase #2	$63.71	11.642%	$71.1271	$71.13	$71.15	$71.10
Purchase #3	$166.46	4.866%	$174.5599	$174.56	$174.55	$174.60
Purchase #4	$181.48	5.344%	$191.1783	$191.18	$191.20	$191.20
Purchase #5	$100.61	13.661%	$114.3543	$114.35	$114.35	$114.40
Purchase #6	$64.70	11.539%	$72.1657	$72.17	$72.15	$72.20
Purchase #7	$238.31	5.245%	$250.8094	$250.81	$250.80	$250.80
7 purchase totals =	$985.85		$1,050.6358	$1,050.64	$1,050.65	$1,050.70