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	$91.27	10.556%	$100.9045	$100.90	$100.90	$100.90
Purchase #2	$84.37	8.506%	$91.5465	$91.55	$91.55	$91.50
Purchase #3	$82.58	12.338%	$92.7687	$92.77	$92.75	$92.80
Purchase #4	$190.88	12.841%	$215.3909	$215.39	$215.40	$215.40
Purchase #5	$119.57	13.148%	$135.2911	$135.29	$135.30	$135.30
Purchase #6	$61.76	8.752%	$67.1652	$67.17	$67.15	$67.20
Purchase #7	$75.28	9.245%	$82.2396	$82.24	$82.25	$82.20
7 purchase totals =	$705.71		$785.3065	$785.31	$785.30	$785.30