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 $213.75   6.775%   $228.2316   $228.23   $228.25   $228.20  
  Purchase #2 $55.81   12.753%   $62.9274   $62.93   $62.95   $62.90  
  Purchase #3 $218.43   3.134%   $225.2756   $225.28   $225.30   $225.30  
  Purchase #4 $9.56   12.673%   $10.7715   $10.77   $10.75   $10.80  
  Purchase #5 $56.26   7.697%   $60.5903   $60.59   $60.60   $60.60  
  Purchase #6 $28.66   7.629%   $30.8465   $30.85   $30.85   $30.80  
  Purchase #7 $168.41   8.874%   $183.3547   $183.35   $183.35   $183.40  
  7 purchase totals = $750.88       $801.9976   $802.00   $802.05   $802.00