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 $51.67   10.269%   $56.976   $56.98   $57.00   $57.00  
  Purchase #2 $100.43   13.408%   $113.8957   $113.90   $113.90   $113.90  
  Purchase #3 $62.92   8.558%   $68.3047   $68.30   $68.30   $68.30  
  Purchase #4 $144.78   13.303%   $164.0401   $164.04   $164.05   $164.00  
  Purchase #5 $219.66   12.786%   $247.7457   $247.75   $247.75   $247.70  
  Purchase #6 $240.75   8.235%   $260.5758   $260.58   $260.60   $260.60  
  Purchase #7 $155.33   12.164%   $174.2243   $174.22   $174.20   $174.20  
  7 purchase totals = $975.54       $1,085.7623   $1,085.77   $1,085.80   $1,085.70