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 $55.65   5.642%   $58.7898   $58.79   $58.80   $58.80  
  Purchase #2 $166.86   5.269%   $175.6519   $175.65   $175.65   $175.70  
  Purchase #3 $222.37   12.493%   $250.1507   $250.15   $250.15   $250.20  
  Purchase #4 $59.86   11.703%   $66.8654   $66.87   $66.85   $66.90  
  Purchase #5 $212.38   6.350%   $225.8661   $225.87   $225.85   $225.90  
  Purchase #6 $121.59   10.640%   $134.5272   $134.53   $134.55   $134.50  
  Purchase #7 $11.46   13.574%   $13.0156   $13.02   $13.00   $13.00  
  7 purchase totals = $850.17       $924.8667   $924.88   $924.85   $925.00