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 $226.50   13.841%   $257.8499   $257.85   $257.85   $257.80  
  Purchase #2 $156.49   12.357%   $175.8275   $175.83   $175.85   $175.80  
  Purchase #3 $31.27   12.139%   $35.0659   $35.07   $35.05   $35.10  
  Purchase #4 $204.96   10.597%   $226.6796   $226.68   $226.70   $226.70  
  Purchase #5 $167.28   3.613%   $173.3238   $173.32   $173.30   $173.30  
  Purchase #6 $26.25   8.357%   $28.4437   $28.44   $28.45   $28.40  
  Purchase #7 $152.88   5.215%   $160.8527   $160.85   $160.85   $160.90  
  7 purchase totals = $965.63       $1,058.0431   $1,058.04   $1,058.05   $1,058.00