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 $223.47   10.256%   $246.3891   $246.39   $246.40   $246.40  
  Purchase #2 $142.46   6.455%   $151.6558   $151.66   $151.65   $151.70  
  Purchase #3 $68.49   7.823%   $73.848   $73.85   $73.85   $73.80  
  Purchase #4 $86.94   10.334%   $95.9244   $95.92   $95.90   $95.90  
  Purchase #5 $16.64   5.618%   $17.5748   $17.57   $17.55   $17.60  
  Purchase #6 $170.30   6.842%   $181.9519   $181.95   $181.95   $182.00  
  Purchase #7 $196.35   6.220%   $208.563   $208.56   $208.55   $208.60  
  7 purchase totals = $904.65       $975.9070   $975.90   $975.85   $976.00