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 $137.41   12.738%   $154.9133   $154.91   $154.90   $154.90  
  Purchase #2 $219.70   6.479%   $233.9344   $233.93   $233.95   $233.90  
  Purchase #3 $217.30   13.619%   $246.8941   $246.89   $246.90   $246.90  
  Purchase #4 $159.97   10.695%   $177.0788   $177.08   $177.10   $177.10  
  Purchase #5 $103.53   10.623%   $114.528   $114.53   $114.55   $114.50  
  Purchase #6 $50.94   11.657%   $56.8781   $56.88   $56.90   $56.90  
  Purchase #7 $166.73   9.149%   $181.9841   $181.98   $182.00   $182.00  
  7 purchase totals = $1,055.58       $1,166.2108   $1,166.20   $1,166.30   $1,166.20