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 $24.58   6.782%   $26.247   $26.25   $26.25   $26.20  
  Purchase #2 $138.90   11.249%   $154.5249   $154.52   $154.50   $154.50  
  Purchase #3 $207.80   13.644%   $236.1522   $236.15   $236.15   $236.20  
  Purchase #4 $25.95   13.852%   $29.5446   $29.54   $29.55   $29.50  
  Purchase #5 $212.32   10.699%   $235.0361   $235.04   $235.05   $235.00  
  Purchase #6 $156.61   12.487%   $176.1659   $176.17   $176.15   $176.20  
  Purchase #7 $155.41   8.488%   $168.6012   $168.60   $168.60   $168.60  
  7 purchase totals = $921.57       $1,026.2719   $1,026.27   $1,026.25   $1,026.20