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 $67.53   10.122%   $74.3654   $74.37   $74.35   $74.40  
  Purchase #2 $186.94   13.246%   $211.7021   $211.70   $211.70   $211.70  
  Purchase #3 $23.58   10.793%   $26.125   $26.13   $26.15   $26.10  
  Purchase #4 $110.34   11.410%   $122.9298   $122.93   $122.95   $122.90  
  Purchase #5 $143.56   8.814%   $156.2134   $156.21   $156.20   $156.20  
  Purchase #6 $224.82   11.558%   $250.8047   $250.80   $250.80   $250.80  
  Purchase #7 $17.74   4.727%   $18.5786   $18.58   $18.60   $18.60  
  7 purchase totals = $774.51       $860.7190   $860.72   $860.75   $860.70