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 $52.42   12.480%   $58.962   $58.96   $58.95   $59.00  
  Purchase #2 $182.32   11.634%   $203.5311   $203.53   $203.55   $203.50  
  Purchase #3 $169.63   13.493%   $192.5182   $192.52   $192.50   $192.50  
  Purchase #4 $106.69   8.780%   $116.0574   $116.06   $116.05   $116.10  
  Purchase #5 $167.65   5.841%   $177.4424   $177.44   $177.45   $177.40  
  Purchase #6 $11.27   11.763%   $12.5957   $12.60   $12.60   $12.60  
  Purchase #7 $208.61   3.532%   $215.9781   $215.98   $216.00   $216.00  
  7 purchase totals = $898.59       $977.0849   $977.09   $977.10   $977.10