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 $49.83   8.536%   $54.0835   $54.08   $54.10   $54.10  
  Purchase #2 $10.86   4.477%   $11.3462   $11.35   $11.35   $11.30  
  Purchase #3 $248.77   11.425%   $277.192   $277.19   $277.20   $277.20  
  Purchase #4 $236.93   9.660%   $259.8174   $259.82   $259.80   $259.80  
  Purchase #5 $175.57   11.298%   $195.4059   $195.41   $195.40   $195.40  
  Purchase #6 $19.41   12.119%   $21.7623   $21.76   $21.75   $21.80  
  Purchase #7 $232.69   9.596%   $255.0189   $255.02   $255.00   $255.00  
  7 purchase totals = $974.06       $1,074.6262   $1,074.63   $1,074.60   $1,074.60