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	$191.75	6.653%	$204.5071	$204.51	$204.50	$204.50
Purchase #2	$45.96	10.531%	$50.8	$50.80	$50.80	$50.80
Purchase #3	$231.51	5.140%	$243.4096	$243.41	$243.40	$243.40
Purchase #4	$52.80	12.646%	$59.4771	$59.48	$59.50	$59.50
Purchase #5	$102.90	12.496%	$115.7584	$115.76	$115.75	$115.80
Purchase #6	$231.98	7.808%	$250.093	$250.09	$250.10	$250.10
Purchase #7	$148.29	12.698%	$167.1199	$167.12	$167.10	$167.10
7 purchase totals =	$1,005.19		$1,091.1651	$1,091.17	$1,091.15	$1,091.20