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	$89.37	11.152%	$99.3365	$99.34	$99.35	$99.30
Purchase #2	$240.75	11.653%	$268.8046	$268.80	$268.80	$268.80
Purchase #3	$165.96	13.782%	$188.8326	$188.83	$188.85	$188.80
Purchase #4	$154.73	8.799%	$168.3447	$168.34	$168.35	$168.30
Purchase #5	$167.97	10.142%	$185.0055	$185.01	$185.00	$185.00
Purchase #6	$247.73	8.185%	$268.0067	$268.01	$268.00	$268.00
Purchase #7	$140.41	11.119%	$156.0222	$156.02	$156.00	$156.00
7 purchase totals =	$1,206.92		$1,334.3528	$1,334.35	$1,334.35	$1,334.20