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 $230.78   10.320%   $254.5965   $254.60   $254.60   $254.60  
  Purchase #2 $58.81   7.546%   $63.2478   $63.25   $63.25   $63.20  
  Purchase #3 $23.36   3.541%   $24.1872   $24.19   $24.20   $24.20  
  Purchase #4 $106.37   4.302%   $110.946   $110.95   $110.95   $110.90  
  Purchase #5 $78.36   3.585%   $81.1692   $81.17   $81.15   $81.20  
  Purchase #6 $167.72   6.387%   $178.4323   $178.43   $178.45   $178.40  
  Purchase #7 $216.53   10.398%   $239.0448   $239.04   $239.05   $239.00  
  7 purchase totals = $881.93       $951.6238   $951.63   $951.65   $951.50