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 $63.50   9.588%   $69.5884   $69.59   $69.60   $69.60  
  Purchase #2 $153.83   13.282%   $174.2617   $174.26   $174.25   $174.30  
  Purchase #3 $39.77   4.772%   $41.6678   $41.67   $41.65   $41.70  
  Purchase #4 $92.51   4.705%   $96.8626   $96.86   $96.85   $96.90  
  Purchase #5 $27.28   7.570%   $29.3451   $29.35   $29.35   $29.30  
  Purchase #6 $234.66   11.800%   $262.3499   $262.35   $262.35   $262.30  
  Purchase #7 $168.37   6.691%   $179.6356   $179.64   $179.65   $179.60  
  7 purchase totals = $779.92       $853.7111   $853.72   $853.70   $853.70