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 $249.43   5.871%   $264.074   $264.07   $264.05   $264.10  
  Purchase #2 $240.65   6.443%   $256.1551   $256.16   $256.15   $256.20  
  Purchase #3 $41.47   13.740%   $47.168   $47.17   $47.15   $47.20  
  Purchase #4 $59.42   10.652%   $65.7494   $65.75   $65.75   $65.70  
  Purchase #5 $133.63   3.238%   $137.9569   $137.96   $137.95   $138.00  
  Purchase #6 $53.93   9.317%   $58.9547   $58.95   $58.95   $59.00  
  Purchase #7 $248.80   11.444%   $277.2727   $277.27   $277.25   $277.30  
  7 purchase totals = $1,027.33       $1,107.3308   $1,107.33   $1,107.25   $1,107.50