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 $234.50   11.789%   $262.1452   $262.15   $262.15   $262.10  
  Purchase #2 $61.44   3.611%   $63.6586   $63.66   $63.65   $63.70  
  Purchase #3 $131.49   9.177%   $143.5568   $143.56   $143.55   $143.60  
  Purchase #4 $61.34   10.746%   $67.9316   $67.93   $67.95   $67.90  
  Purchase #5 $181.88   10.648%   $201.2466   $201.25   $201.25   $201.20  
  Purchase #6 $64.68   9.462%   $70.8   $70.80   $70.80   $70.80  
  Purchase #7 $106.84   4.367%   $111.5057   $111.51   $111.50   $111.50  
  7 purchase totals = $842.17       $920.8445   $920.86   $920.85   $920.80