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 $76.60   13.515%   $86.9525   $86.95   $86.95   $87.00  
  Purchase #2 $23.81   6.806%   $25.4305   $25.43   $25.45   $25.40  
  Purchase #3 $145.35   4.616%   $152.0594   $152.06   $152.05   $152.10  
  Purchase #4 $86.47   7.567%   $93.0132   $93.01   $93.00   $93.00  
  Purchase #5 $60.46   11.525%   $67.428   $67.43   $67.45   $67.40  
  Purchase #6 $115.88   3.558%   $120.003   $120.00   $120.00   $120.00  
  Purchase #7 $32.87   5.119%   $34.5526   $34.55   $34.55   $34.60  
  7 purchase totals = $541.44       $579.4392   $579.43   $579.45   $579.50