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	$54.59	4.227%	$56.8975	$56.90	$56.90	$56.90
Purchase #2	$141.30	8.351%	$153.1	$153.10	$153.10	$153.10
Purchase #3	$63.55	5.615%	$67.1183	$67.12	$67.10	$67.10
Purchase #4	$175.27	11.433%	$195.3086	$195.31	$195.30	$195.30
Purchase #5	$58.74	4.824%	$61.5736	$61.57	$61.55	$61.60
Purchase #6	$91.86	5.355%	$96.7791	$96.78	$96.80	$96.80
Purchase #7	$168.48	12.370%	$189.321	$189.32	$189.30	$189.30
7 purchase totals =	$753.79		$820.0981	$820.10	$820.05	$820.10