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 $88.39   8.223%   $95.6583   $95.66   $95.65   $95.70  
  Purchase #2 $49.83   7.515%   $53.5747   $53.57   $53.55   $53.60  
  Purchase #3 $219.94   3.214%   $227.0089   $227.01   $227.00   $227.00  
  Purchase #4 $35.94   4.723%   $37.6374   $37.64   $37.65   $37.60  
  Purchase #5 $211.42   8.195%   $228.7459   $228.75   $228.75   $228.70  
  Purchase #6 $73.75   10.582%   $81.5542   $81.55   $81.55   $81.60  
  Purchase #7 $74.64   4.631%   $78.0966   $78.10   $78.10   $78.10  
  7 purchase totals = $753.91       $802.2760   $802.28   $802.25   $802.30