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 $33.55   13.457%   $38.0648   $38.06   $38.05   $38.10  
  Purchase #2 $161.54   7.675%   $173.9382   $173.94   $173.95   $173.90  
  Purchase #3 $56.46   10.139%   $62.1845   $62.18   $62.20   $62.20  
  Purchase #4 $197.41   10.153%   $217.453   $217.45   $217.45   $217.50  
  Purchase #5 $56.67   3.575%   $58.696   $58.70   $58.70   $58.70  
  Purchase #6 $145.55   6.132%   $154.4751   $154.48   $154.50   $154.50  
  Purchase #7 $70.45   13.778%   $80.1566   $80.16   $80.15   $80.20  
  7 purchase totals = $721.63       $784.9682   $784.97   $785.00   $785.10