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 $176.65   9.343%   $193.1544   $193.15   $193.15   $193.20  
  Purchase #2 $228.68   8.423%   $247.9417   $247.94   $247.95   $247.90  
  Purchase #3 $247.98   4.394%   $258.8762   $258.88   $258.90   $258.90  
  Purchase #4 $5.32   9.212%   $5.8101   $5.81   $5.80   $5.80  
  Purchase #5 $105.51   11.583%   $117.7312   $117.73   $117.75   $117.70  
  Purchase #6 $30.33   3.793%   $31.4804   $31.48   $31.50   $31.50  
  Purchase #7 $58.65   7.335%   $62.952   $62.95   $62.95   $63.00  
  7 purchase totals = $853.12       $917.9460   $917.94   $918.00   $918.00