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 $191.74   11.585%   $213.9531   $213.95   $213.95   $214.00  
  Purchase #2 $87.78   12.655%   $98.8886   $98.89   $98.90   $98.90  
  Purchase #3 $48.90   4.732%   $51.2139   $51.21   $51.20   $51.20  
  Purchase #4 $88.34   12.616%   $99.485   $99.49   $99.50   $99.50  
  Purchase #5 $186.79   6.371%   $198.6904   $198.69   $198.70   $198.70  
  Purchase #6 $74.33   8.849%   $80.9075   $80.91   $80.90   $80.90  
  Purchase #7 $238.33   7.275%   $255.6685   $255.67   $255.65   $255.70  
  7 purchase totals = $916.21       $998.8070   $998.81   $998.80   $998.90