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 $249.88   4.856%   $262.0142   $262.01   $262.00   $262.00  
  Purchase #2 $14.41   3.603%   $14.9292   $14.93   $14.95   $14.90  
  Purchase #3 $41.26   4.242%   $43.0102   $43.01   $43.00   $43.00  
  Purchase #4 $38.74   7.308%   $41.5711   $41.57   $41.55   $41.60  
  Purchase #5 $81.63   7.265%   $87.5604   $87.56   $87.55   $87.60  
  Purchase #6 $105.34   7.582%   $113.3269   $113.33   $113.35   $113.30  
  Purchase #7 $229.79   3.526%   $237.8924   $237.89   $237.90   $237.90  
  7 purchase totals = $761.05       $800.3044   $800.30   $800.30   $800.30