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 $161.34   8.154%   $174.4957   $174.50   $174.50   $174.50  
  Purchase #2 $21.95   9.433%   $24.0205   $24.02   $24.00   $24.00  
  Purchase #3 $41.93   11.118%   $46.5918   $46.59   $46.60   $46.60  
  Purchase #4 $119.74   7.780%   $129.0558   $129.06   $129.05   $129.10  
  Purchase #5 $243.60   10.565%   $269.3363   $269.34   $269.35   $269.30  
  Purchase #6 $54.82   11.320%   $61.0256   $61.03   $61.05   $61.00  
  Purchase #7 $84.87   7.852%   $91.534   $91.53   $91.55   $91.50  
  7 purchase totals = $728.25       $796.0597   $796.07   $796.10   $796.00