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 $76.74   13.186%   $86.8589   $86.86   $86.85   $86.90  
  Purchase #2 $239.65   12.323%   $269.1821   $269.18   $269.20   $269.20  
  Purchase #3 $174.40   5.129%   $183.345   $183.35   $183.35   $183.30  
  Purchase #4 $87.75   11.488%   $97.8307   $97.83   $97.85   $97.80  
  Purchase #5 $25.65   11.187%   $28.5195   $28.52   $28.50   $28.50  
  Purchase #6 $89.75   8.449%   $97.333   $97.33   $97.35   $97.30  
  Purchase #7 $90.47   6.500%   $96.3506   $96.35   $96.35   $96.40  
  7 purchase totals = $784.41       $859.4198   $859.42   $859.45   $859.40