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 $198.80   6.273%   $211.2707   $211.27   $211.25   $211.30  
  Purchase #2 $54.82   8.843%   $59.6677   $59.67   $59.65   $59.70  
  Purchase #3 $53.86   4.410%   $56.2352   $56.24   $56.25   $56.20  
  Purchase #4 $191.49   3.763%   $198.6958   $198.70   $198.70   $198.70  
  Purchase #5 $243.92   6.106%   $258.8138   $258.81   $258.80   $258.80  
  Purchase #6 $138.47   3.849%   $143.7997   $143.80   $143.80   $143.80  
  Purchase #7 $32.49   7.162%   $34.8169   $34.82   $34.80   $34.80  
  7 purchase totals = $913.85       $963.2998   $963.31   $963.25   $963.30