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 $56.51   12.662%   $63.6653   $63.67   $63.65   $63.70  
  Purchase #2 $18.93   3.394%   $19.5725   $19.57   $19.55   $19.60  
  Purchase #3 $201.87   5.172%   $212.3107   $212.31   $212.30   $212.30  
  Purchase #4 $173.80   8.213%   $188.0742   $188.07   $188.05   $188.10  
  Purchase #5 $224.67   6.417%   $239.0871   $239.09   $239.10   $239.10  
  Purchase #6 $249.84   10.226%   $275.3886   $275.39   $275.40   $275.40  
  Purchase #7 $35.69   6.773%   $38.1073   $38.11   $38.10   $38.10  
  7 purchase totals = $961.31       $1,036.2057   $1,036.21   $1,036.15   $1,036.30