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 $22.81   7.543%   $24.5306   $24.53   $24.55   $24.50  
  Purchase #2 $137.35   9.407%   $150.2705   $150.27   $150.25   $150.30  
  Purchase #3 $143.58   13.200%   $162.5326   $162.53   $162.55   $162.50  
  Purchase #4 $41.48   7.747%   $44.6935   $44.69   $44.70   $44.70  
  Purchase #5 $201.74   4.219%   $210.2514   $210.25   $210.25   $210.30  
  Purchase #6 $201.89   7.414%   $216.8581   $216.86   $216.85   $216.90  
  Purchase #7 $104.59   10.615%   $115.6922   $115.69   $115.70   $115.70  
  7 purchase totals = $853.44       $924.8289   $924.82   $924.85   $924.90