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 $247.99   6.550%   $264.2333   $264.23   $264.25   $264.20  
  Purchase #2 $108.65   3.475%   $112.4256   $112.43   $112.45   $112.40  
  Purchase #3 $201.52   3.651%   $208.8775   $208.88   $208.90   $208.90  
  Purchase #4 $53.44   7.546%   $57.4726   $57.47   $57.45   $57.50  
  Purchase #5 $244.26   12.317%   $274.3455   $274.35   $274.35   $274.30  
  Purchase #6 $65.88   5.456%   $69.4744   $69.47   $69.45   $69.50  
  Purchase #7 $165.50   4.358%   $172.7125   $172.71   $172.70   $172.70  
  7 purchase totals = $1,087.24       $1,159.5414   $1,159.54   $1,159.55   $1,159.50