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 $182.67   10.380%   $201.6311   $201.63   $201.65   $201.60  
  Purchase #2 $69.81   9.157%   $76.2025   $76.20   $76.20   $76.20  
  Purchase #3 $188.29   8.156%   $203.6469   $203.65   $203.65   $203.60  
  Purchase #4 $130.80   5.265%   $137.6866   $137.69   $137.70   $137.70  
  Purchase #5 $96.84   5.224%   $101.8989   $101.90   $101.90   $101.90  
  Purchase #6 $26.51   3.873%   $27.5367   $27.54   $27.55   $27.50  
  Purchase #7 $104.61   3.753%   $108.536   $108.54   $108.55   $108.50  
  7 purchase totals = $799.53       $857.1387   $857.15   $857.20   $857.00