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 $162.69   13.143%   $184.0723   $184.07   $184.05   $184.10  
  Purchase #2 $156.92   3.196%   $161.9352   $161.94   $161.95   $161.90  
  Purchase #3 $90.29   12.737%   $101.7902   $101.79   $101.80   $101.80  
  Purchase #4 $76.97   5.257%   $81.0163   $81.02   $81.00   $81.00  
  Purchase #5 $22.68   7.558%   $24.3942   $24.39   $24.40   $24.40  
  Purchase #6 $217.91   13.752%   $247.877   $247.88   $247.90   $247.90  
  Purchase #7 $220.48   3.449%   $228.0844   $228.08   $228.10   $228.10  
  7 purchase totals = $947.94       $1,029.1696   $1,029.17   $1,029.20   $1,029.20