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	$73.33	6.786%	$78.3062	$78.31	$78.30	$78.30
Purchase #2	$209.94	5.767%	$222.0472	$222.05	$222.05	$222.00
Purchase #3	$220.65	10.873%	$244.6413	$244.64	$244.65	$244.60
Purchase #4	$226.78	3.794%	$235.384	$235.38	$235.40	$235.40
Purchase #5	$88.38	11.593%	$98.6259	$98.63	$98.65	$98.60
Purchase #6	$135.33	8.467%	$146.7884	$146.79	$146.80	$146.80
Purchase #7	$86.56	3.844%	$89.8874	$89.89	$89.90	$89.90
7 purchase totals =	$1,040.97		$1,115.6804	$1,115.69	$1,115.75	$1,115.60