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 $87.58   8.239%   $94.7957   $94.80   $94.80   $94.80  
  Purchase #2 $164.66   13.239%   $186.4593   $186.46   $186.45   $186.50  
  Purchase #3 $230.28   12.421%   $258.8831   $258.88   $258.90   $258.90  
  Purchase #4 $18.94   3.561%   $19.6145   $19.61   $19.60   $19.60  
  Purchase #5 $199.29   6.728%   $212.6982   $212.70   $212.70   $212.70  
  Purchase #6 $211.90   7.767%   $228.3583   $228.36   $228.35   $228.40  
  Purchase #7 $39.88   5.588%   $42.1085   $42.11   $42.10   $42.10  
  7 purchase totals = $952.53       $1,042.9176   $1,042.92   $1,042.90   $1,043.00