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	$11.77	4.744%	$12.3284	$12.33	$12.35	$12.30
Purchase #2	$73.59	12.530%	$82.8108	$82.81	$82.80	$82.80
Purchase #3	$170.73	12.252%	$191.6478	$191.65	$191.65	$191.60
Purchase #4	$212.90	7.691%	$229.2741	$229.27	$229.25	$229.30
Purchase #5	$231.34	12.223%	$259.6167	$259.62	$259.60	$259.60
Purchase #6	$81.62	12.427%	$91.7629	$91.76	$91.75	$91.80
Purchase #7	$152.25	9.506%	$166.7229	$166.72	$166.70	$166.70
7 purchase totals =	$934.20		$1,034.1636	$1,034.16	$1,034.10	$1,034.10