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 $234.60   11.260%   $261.016   $261.02   $261.00   $261.00  
  Purchase #2 $39.60   12.568%   $44.5769   $44.58   $44.60   $44.60  
  Purchase #3 $56.78   7.826%   $61.2236   $61.22   $61.20   $61.20  
  Purchase #4 $65.88   10.590%   $72.8567   $72.86   $72.85   $72.90  
  Purchase #5 $150.28   10.340%   $165.819   $165.82   $165.80   $165.80  
  Purchase #6 $246.44   8.263%   $266.8033   $266.80   $266.80   $266.80  
  Purchase #7 $86.78   11.535%   $96.7901   $96.79   $96.80   $96.80  
  7 purchase totals = $880.36       $969.0856   $969.09   $969.05   $969.10