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 $38.73   11.680%   $43.2537   $43.25   $43.25   $43.30  
  Purchase #2 $208.45   12.597%   $234.7084   $234.71   $234.70   $234.70  
  Purchase #3 $106.90   10.451%   $118.0721   $118.07   $118.05   $118.10  
  Purchase #4 $165.65   9.758%   $181.8141   $181.81   $181.80   $181.80  
  Purchase #5 $174.27   6.780%   $186.0855   $186.09   $186.10   $186.10  
  Purchase #6 $59.66   10.787%   $66.0955   $66.10   $66.10   $66.10  
  Purchase #7 $64.44   10.186%   $71.0039   $71.00   $71.00   $71.00  
  7 purchase totals = $818.10       $901.0332   $901.03   $901.00   $901.10