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 $53.53   4.677%   $56.0336   $56.03   $56.05   $56.00  
  Purchase #2 $217.92   13.474%   $247.2825   $247.28   $247.30   $247.30  
  Purchase #3 $50.70   7.777%   $54.6429   $54.64   $54.65   $54.60  
  Purchase #4 $198.36   5.185%   $208.645   $208.65   $208.65   $208.60  
  Purchase #5 $161.79   9.188%   $176.6553   $176.66   $176.65   $176.70  
  Purchase #6 $216.26   8.531%   $234.7091   $234.71   $234.70   $234.70  
  Purchase #7 $16.36   9.416%   $17.9005   $17.90   $17.90   $17.90  
  7 purchase totals = $914.92       $995.8689   $995.87   $995.90   $995.80