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 $77.95   11.466%   $86.8877   $86.89   $86.90   $86.90  
  Purchase #2 $247.29   10.557%   $273.3964   $273.40   $273.40   $273.40  
  Purchase #3 $59.86   13.520%   $67.9531   $67.95   $67.95   $68.00  
  Purchase #4 $193.91   12.664%   $218.4668   $218.47   $218.45   $218.50  
  Purchase #5 $201.61   13.789%   $229.41   $229.41   $229.40   $229.40  
  Purchase #6 $218.57   9.244%   $238.7746   $238.77   $238.75   $238.80  
  Purchase #7 $213.36   6.122%   $226.4219   $226.42   $226.40   $226.40  
  7 purchase totals = $1,212.55       $1,341.3105   $1,341.31   $1,341.25   $1,341.40