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	$73.55	6.812%	$78.5602	$78.56	$78.55	$78.60
Purchase #2	$228.48	11.851%	$255.5572	$255.56	$255.55	$255.60
Purchase #3	$212.28	9.672%	$232.8117	$232.81	$232.80	$232.80
Purchase #4	$39.86	6.108%	$42.2946	$42.29	$42.30	$42.30
Purchase #5	$64.29	11.438%	$71.6435	$71.64	$71.65	$71.60
Purchase #6	$212.29	10.331%	$234.2217	$234.22	$234.20	$234.20
Purchase #7	$189.74	4.804%	$198.8551	$198.86	$198.85	$198.90
7 purchase totals =	$1,020.49		$1,113.9440	$1,113.94	$1,113.90	$1,114.00