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	$59.82	7.586%	$64.3579	$64.36	$64.35	$64.40
Purchase #2	$224.55	13.708%	$255.3313	$255.33	$255.35	$255.30
Purchase #3	$98.27	12.690%	$110.7405	$110.74	$110.75	$110.70
Purchase #4	$130.33	13.851%	$148.382	$148.38	$148.40	$148.40
Purchase #5	$67.39	6.661%	$71.8788	$71.88	$71.90	$71.90
Purchase #6	$107.27	10.446%	$118.4754	$118.48	$118.50	$118.50
Purchase #7	$63.71	8.578%	$69.175	$69.18	$69.20	$69.20
7 purchase totals =	$751.34		$838.3409	$838.35	$838.45	$838.40