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 $228.49   11.607%   $255.0108   $255.01   $255.00   $255.00  
  Purchase #2 $239.47   12.613%   $269.6744   $269.67   $269.65   $269.70  
  Purchase #3 $233.95   6.115%   $248.256   $248.26   $248.25   $248.30  
  Purchase #4 $166.53   7.447%   $178.9315   $178.93   $178.95   $178.90  
  Purchase #5 $70.87   9.550%   $77.6381   $77.64   $77.65   $77.60  
  Purchase #6 $181.92   11.726%   $203.2519   $203.25   $203.25   $203.30  
  Purchase #7 $223.53   11.418%   $249.0527   $249.05   $249.05   $249.10  
  7 purchase totals = $1,344.76       $1,481.8154   $1,481.81   $1,481.80   $1,481.90