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 $249.31   10.717%   $276.0286   $276.03   $276.05   $276.00  
  Purchase #2 $105.78   12.547%   $119.0522   $119.05   $119.05   $119.10  
  Purchase #3 $203.95   12.260%   $228.9543   $228.95   $228.95   $229.00  
  Purchase #4 $39.53   7.837%   $42.628   $42.63   $42.65   $42.60  
  Purchase #5 $146.91   10.342%   $162.1034   $162.10   $162.10   $162.10  
  Purchase #6 $199.45   4.232%   $207.8907   $207.89   $207.90   $207.90  
  Purchase #7 $81.48   13.626%   $92.5825   $92.58   $92.60   $92.60  
  7 purchase totals = $1,026.41       $1,129.2397   $1,129.23   $1,129.30   $1,129.30