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	$233.84	3.639%	$242.3494	$242.35	$242.35	$242.30
Purchase #2	$48.59	7.769%	$52.365	$52.37	$52.35	$52.40
Purchase #3	$28.52	9.108%	$31.1176	$31.12	$31.10	$31.10
Purchase #4	$183.33	7.197%	$196.5243	$196.52	$196.50	$196.50
Purchase #5	$85.39	3.691%	$88.5417	$88.54	$88.55	$88.50
Purchase #6	$96.63	10.415%	$106.694	$106.69	$106.70	$106.70
Purchase #7	$179.25	3.684%	$185.8536	$185.85	$185.85	$185.90
7 purchase totals =	$855.55		$903.4456	$903.44	$903.40	$903.40