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 $246.87   4.798%   $258.7148   $258.71   $258.70   $258.70  
  Purchase #2 $96.91   4.782%   $101.5442   $101.54   $101.55   $101.50  
  Purchase #3 $6.93   5.759%   $7.3291   $7.33   $7.35   $7.30  
  Purchase #4 $90.41   6.350%   $96.151   $96.15   $96.15   $96.20  
  Purchase #5 $201.95   9.220%   $220.5698   $220.57   $220.55   $220.60  
  Purchase #6 $248.37   7.735%   $267.5814   $267.58   $267.60   $267.60  
  Purchase #7 $113.33   9.849%   $124.4919   $124.49   $124.50   $124.50  
  7 purchase totals = $1,004.77       $1,076.3822   $1,076.37   $1,076.40   $1,076.40