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	$37.38	12.117%	$41.9093	$41.91	$41.90	$41.90
Purchase #2	$232.25	3.567%	$240.5344	$240.53	$240.55	$240.50
Purchase #3	$221.63	7.533%	$238.3254	$238.33	$238.35	$238.30
Purchase #4	$166.70	4.550%	$174.2849	$174.28	$174.30	$174.30
Purchase #5	$208.63	7.107%	$223.4573	$223.46	$223.45	$223.50
Purchase #6	$25.98	9.675%	$28.4936	$28.49	$28.50	$28.50
Purchase #7	$232.39	4.735%	$243.3937	$243.39	$243.40	$243.40
7 purchase totals =	$1,124.96		$1,190.3986	$1,190.39	$1,190.45	$1,190.40