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 $76.64   10.700%   $84.8405   $84.84   $84.85   $84.80  
  Purchase #2 $60.46   11.192%   $67.2267   $67.23   $67.25   $67.20  
  Purchase #3 $145.51   6.679%   $155.2286   $155.23   $155.25   $155.20  
  Purchase #4 $176.89   9.567%   $193.8131   $193.81   $193.80   $193.80  
  Purchase #5 $24.76   4.452%   $25.8623   $25.86   $25.85   $25.90  
  Purchase #6 $217.49   13.542%   $246.9425   $246.94   $246.95   $246.90  
  Purchase #7 $222.87   12.179%   $250.0133   $250.01   $250.00   $250.00  
  7 purchase totals = $924.62       $1,023.9270   $1,023.92   $1,023.95   $1,023.80