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 $143.90   13.425%   $163.2186   $163.22   $163.20   $163.20  
  Purchase #2 $31.88   5.134%   $33.5167   $33.52   $33.50   $33.50  
  Purchase #3 $35.33   6.438%   $37.6045   $37.60   $37.60   $37.60  
  Purchase #4 $135.67   3.493%   $140.409   $140.41   $140.40   $140.40  
  Purchase #5 $8.50   5.133%   $8.9363   $8.94   $8.95   $8.90  
  Purchase #6 $122.83   6.118%   $130.3447   $130.34   $130.35   $130.30  
  Purchase #7 $126.63   12.767%   $142.7969   $142.80   $142.80   $142.80  
  7 purchase totals = $604.74       $656.8267   $656.83   $656.80   $656.70