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 $142.59   8.382%   $154.5419   $154.54   $154.55   $154.50  
  Purchase #2 $182.28   10.566%   $201.5397   $201.54   $201.55   $201.50  
  Purchase #3 $15.85   13.293%   $17.9569   $17.96   $17.95   $18.00  
  Purchase #4 $91.93   10.229%   $101.3335   $101.33   $101.35   $101.30  
  Purchase #5 $227.92   10.826%   $252.5946   $252.59   $252.60   $252.60  
  Purchase #6 $241.65   9.232%   $263.9591   $263.96   $263.95   $264.00  
  Purchase #7 $207.66   10.874%   $230.2409   $230.24   $230.25   $230.20  
  7 purchase totals = $1,109.88       $1,222.1666   $1,222.16   $1,222.20   $1,222.10