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 $246.50   7.259%   $264.3934   $264.39   $264.40   $264.40  
  Purchase #2 $15.36   12.850%   $17.3338   $17.33   $17.35   $17.30  
  Purchase #3 $155.56   10.396%   $171.732   $171.73   $171.75   $171.70  
  Purchase #4 $23.85   12.358%   $26.7974   $26.80   $26.80   $26.80  
  Purchase #5 $178.53   6.296%   $189.7702   $189.77   $189.75   $189.80  
  Purchase #6 $69.67   13.240%   $78.8943   $78.89   $78.90   $78.90  
  Purchase #7 $192.30   4.654%   $201.2496   $201.25   $201.25   $201.20  
  7 purchase totals = $881.77       $950.1707   $950.16   $950.20   $950.10