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	$227.75	3.742%	$236.2724	$236.27	$236.25	$236.30
Purchase #2	$248.34	8.484%	$269.4092	$269.41	$269.40	$269.40
Purchase #3	$36.29	4.154%	$37.7975	$37.80	$37.80	$37.80
Purchase #4	$219.71	13.663%	$249.729	$249.73	$249.75	$249.70
Purchase #5	$243.82	8.637%	$264.8787	$264.88	$264.90	$264.90
Purchase #6	$115.50	7.260%	$123.8853	$123.89	$123.90	$123.90
Purchase #7	$178.27	7.353%	$191.3782	$191.38	$191.40	$191.40
7 purchase totals =	$1,269.68		$1,373.3503	$1,373.36	$1,373.40	$1,373.40