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 $166.61   5.245%   $175.3487   $175.35   $175.35   $175.30  
  Purchase #2 $181.50   10.558%   $200.6628   $200.66   $200.65   $200.70  
  Purchase #3 $216.47   6.106%   $229.6877   $229.69   $229.70   $229.70  
  Purchase #4 $78.60   7.603%   $84.576   $84.58   $84.60   $84.60  
  Purchase #5 $33.46   4.807%   $35.0684   $35.07   $35.05   $35.10  
  Purchase #6 $193.64   3.844%   $201.0835   $201.08   $201.10   $201.10  
  Purchase #7 $125.41   5.110%   $131.8185   $131.82   $131.80   $131.80  
  7 purchase totals = $995.69       $1,058.2456   $1,058.25   $1,058.25   $1,058.30