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	$87.34	13.526%	$99.1536	$99.15	$99.15	$99.20
Purchase #2	$178.36	7.302%	$191.3838	$191.38	$191.40	$191.40
Purchase #3	$181.53	7.292%	$194.7672	$194.77	$194.75	$194.80
Purchase #4	$33.68	4.460%	$35.1821	$35.18	$35.20	$35.20
Purchase #5	$82.51	3.524%	$85.4177	$85.42	$85.40	$85.40
Purchase #6	$215.73	12.830%	$243.4082	$243.41	$243.40	$243.40
Purchase #7	$53.27	12.565%	$59.9634	$59.96	$59.95	$60.00
7 purchase totals =	$832.42		$909.2760	$909.27	$909.25	$909.40