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 $222.61   8.587%   $241.7255   $241.73   $241.75   $241.70  
  Purchase #2 $86.45   7.671%   $93.0816   $93.08   $93.10   $93.10  
  Purchase #3 $21.78   6.449%   $23.1846   $23.18   $23.20   $23.20  
  Purchase #4 $201.85   12.432%   $226.944   $226.94   $226.95   $226.90  
  Purchase #5 $129.85   6.588%   $138.4045   $138.40   $138.40   $138.40  
  Purchase #6 $200.59   10.152%   $220.9539   $220.95   $220.95   $221.00  
  Purchase #7 $73.25   7.595%   $78.8133   $78.81   $78.80   $78.80  
  7 purchase totals = $936.38       $1,023.1074   $1,023.09   $1,023.15   $1,023.10