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 $237.26   9.832%   $260.5874   $260.59   $260.60   $260.60  
  Purchase #2 $196.93   10.187%   $216.9913   $216.99   $217.00   $217.00  
  Purchase #3 $17.95   10.437%   $19.8234   $19.82   $19.80   $19.80  
  Purchase #4 $234.45   10.206%   $258.378   $258.38   $258.40   $258.40  
  Purchase #5 $49.39   13.275%   $55.9465   $55.95   $55.95   $55.90  
  Purchase #6 $51.44   10.135%   $56.6534   $56.65   $56.65   $56.70  
  Purchase #7 $230.54   7.795%   $248.5106   $248.51   $248.50   $248.50  
  7 purchase totals = $1,017.96       $1,116.8906   $1,116.89   $1,116.90   $1,116.90