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 $242.89   13.596%   $275.9133   $275.91   $275.90   $275.90  
  Purchase #2 $42.86   8.702%   $46.5897   $46.59   $46.60   $46.60  
  Purchase #3 $48.53   3.373%   $50.1669   $50.17   $50.15   $50.20  
  Purchase #4 $201.44   5.232%   $211.9793   $211.98   $212.00   $212.00  
  Purchase #5 $71.44   9.870%   $78.4911   $78.49   $78.50   $78.50  
  Purchase #6 $5.79   3.376%   $5.9855   $5.99   $6.00   $6.00  
  Purchase #7 $207.26   8.745%   $225.3849   $225.38   $225.40   $225.40  
  7 purchase totals = $820.21       $894.5107   $894.51   $894.55   $894.60