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 $177.69   7.772%   $191.5001   $191.50   $191.50   $191.50  
  Purchase #2 $71.47   9.636%   $78.3568   $78.36   $78.35   $78.40  
  Purchase #3 $154.43   4.303%   $161.0751   $161.08   $161.10   $161.10  
  Purchase #4 $7.46   12.735%   $8.41   $8.41   $8.40   $8.40  
  Purchase #5 $90.82   12.589%   $102.2533   $102.25   $102.25   $102.30  
  Purchase #6 $68.49   9.109%   $74.7288   $74.73   $74.75   $74.70  
  Purchase #7 $229.62   6.759%   $245.14   $245.14   $245.15   $245.10  
  7 purchase totals = $799.98       $861.4641   $861.47   $861.50   $861.50