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 $246.46   6.725%   $263.0344   $263.03   $263.05   $263.00  
  Purchase #2 $104.99   10.348%   $115.8544   $115.85   $115.85   $115.90  
  Purchase #3 $201.97   5.349%   $212.7734   $212.77   $212.75   $212.80  
  Purchase #4 $149.45   4.329%   $155.9197   $155.92   $155.90   $155.90  
  Purchase #5 $119.83   13.119%   $135.5505   $135.55   $135.55   $135.60  
  Purchase #6 $239.39   3.642%   $248.1086   $248.11   $248.10   $248.10  
  Purchase #7 $57.79   3.298%   $59.6959   $59.70   $59.70   $59.70  
  7 purchase totals = $1,119.88       $1,190.9369   $1,190.93   $1,190.90   $1,191.00