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 $84.89   13.127%   $96.0335   $96.03   $96.05   $96.00  
  Purchase #2 $189.56   10.214%   $208.9217   $208.92   $208.90   $208.90  
  Purchase #3 $43.80   6.676%   $46.7241   $46.72   $46.70   $46.70  
  Purchase #4 $39.50   9.274%   $43.1632   $43.16   $43.15   $43.20  
  Purchase #5 $175.92   5.785%   $186.097   $186.10   $186.10   $186.10  
  Purchase #6 $26.25   13.814%   $29.8762   $29.88   $29.90   $29.90  
  Purchase #7 $165.30   9.634%   $181.225   $181.23   $181.25   $181.20  
  7 purchase totals = $725.22       $792.0407   $792.04   $792.05   $792.00