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 $24.95   5.302%   $26.2728   $26.27   $26.25   $26.30  
  Purchase #2 $135.33   3.171%   $139.6213   $139.62   $139.60   $139.60  
  Purchase #3 $82.49   12.557%   $92.8483   $92.85   $92.85   $92.80  
  Purchase #4 $139.62   10.402%   $154.1433   $154.14   $154.15   $154.10  
  Purchase #5 $100.69   12.478%   $113.2541   $113.25   $113.25   $113.30  
  Purchase #6 $148.41   8.648%   $161.2445   $161.24   $161.25   $161.20  
  Purchase #7 $227.52   11.190%   $252.9795   $252.98   $253.00   $253.00  
  7 purchase totals = $859.01       $940.3638   $940.35   $940.35   $940.30