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 $121.55   11.848%   $135.9512   $135.95   $135.95   $136.00  
  Purchase #2 $38.73   13.582%   $43.9903   $43.99   $44.00   $44.00  
  Purchase #3 $117.89   11.736%   $131.7256   $131.73   $131.75   $131.70  
  Purchase #4 $56.94   4.385%   $59.4368   $59.44   $59.45   $59.40  
  Purchase #5 $245.75   4.666%   $257.2167   $257.22   $257.20   $257.20  
  Purchase #6 $190.64   13.218%   $215.8388   $215.84   $215.85   $215.80  
  Purchase #7 $156.62   13.248%   $177.369   $177.37   $177.35   $177.40  
  7 purchase totals = $928.12       $1,021.5284   $1,021.54   $1,021.55   $1,021.50