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 $226.44   8.748%   $246.249   $246.25   $246.25   $246.20  
  Purchase #2 $124.93   7.281%   $134.0262   $134.03   $134.05   $134.00  
  Purchase #3 $126.41   13.857%   $143.9266   $143.93   $143.95   $143.90  
  Purchase #4 $29.60   8.297%   $32.0559   $32.06   $32.05   $32.10  
  Purchase #5 $184.64   12.338%   $207.4209   $207.42   $207.40   $207.40  
  Purchase #6 $131.65   8.666%   $143.0588   $143.06   $143.05   $143.10  
  Purchase #7 $247.42   4.791%   $259.2739   $259.27   $259.25   $259.30  
  7 purchase totals = $1,071.09       $1,166.0113   $1,166.02   $1,166.00   $1,166.00