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 $248.85   7.527%   $267.5809   $267.58   $267.60   $267.60  
  Purchase #2 $37.48   5.777%   $39.6452   $39.65   $39.65   $39.60  
  Purchase #3 $90.67   4.723%   $94.9523   $94.95   $94.95   $95.00  
  Purchase #4 $137.56   6.161%   $146.0351   $146.04   $146.05   $146.00  
  Purchase #5 $160.40   9.127%   $175.0397   $175.04   $175.05   $175.00  
  Purchase #6 $203.30   10.554%   $224.7563   $224.76   $224.75   $224.80  
  Purchase #7 $175.85   6.311%   $186.9479   $186.95   $186.95   $186.90  
  7 purchase totals = $1,054.11       $1,134.9574   $1,134.97   $1,135.00   $1,134.90