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 $58.56   8.547%   $63.5651   $63.57   $63.55   $63.60  
  Purchase #2 $163.84   5.782%   $173.3132   $173.31   $173.30   $173.30  
  Purchase #3 $197.43   13.835%   $224.7444   $224.74   $224.75   $224.70  
  Purchase #4 $240.62   7.590%   $258.8831   $258.88   $258.90   $258.90  
  Purchase #5 $8.25   10.346%   $9.1035   $9.10   $9.10   $9.10  
  Purchase #6 $196.49   5.203%   $206.7134   $206.71   $206.70   $206.70  
  Purchase #7 $79.26   13.289%   $89.7929   $89.79   $89.80   $89.80  
  7 purchase totals = $944.45       $1,026.1156   $1,026.10   $1,026.10   $1,026.10