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 $245.70   8.273%   $266.0268   $266.03   $266.05   $266.00  
  Purchase #2 $187.72   8.425%   $203.5354   $203.54   $203.55   $203.50  
  Purchase #3 $189.67   6.160%   $201.3537   $201.35   $201.35   $201.40  
  Purchase #4 $161.72   5.841%   $171.1661   $171.17   $171.15   $171.20  
  Purchase #5 $41.75   9.440%   $45.6912   $45.69   $45.70   $45.70  
  Purchase #6 $55.83   4.449%   $58.3139   $58.31   $58.30   $58.30  
  Purchase #7 $124.70   5.181%   $131.1607   $131.16   $131.15   $131.20  
  7 purchase totals = $1,007.09       $1,077.2478   $1,077.25   $1,077.25   $1,077.30